Systems and methods for conducting electrophysiological testing using high-voltage energy pulses to stun tissue

ABSTRACT

Systems and methods for diagnosing and treating tissue transmit an electrical energy pulse that temporarily stuns a zone of tissue, temporarily rendering it electrically unresponsive. The systems and methods sense an electrophysiological effect due to the transmitted pulse. The systems and methods alter an electrophysiological property of tissue in or near the zone based, at least in part, upon the sensed electrophysiological effect. The alteration of the electrophysiological property can be accomplished, for example, by tissue ablation or by the administration of medication. In a preferred implementation, radio frequency energy is used to both temporarily stun tissue and to ablate tissue through a common electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/430,835, filed Nov. 1, 1999, now U.S. Pat. No. 6,212,426, which is acontinuation of U.S. application Ser. No. 09/084,065, filed May 22,1998, now U.S. Pat. No. 6,023,638, which is a continuation-in-part ofU.S. application Ser. No. 08/914,860, filed Aug. 19, 1997, now U.S. Pat.No. 5,759,158, which is a continuation of U.S. application Ser. No.08/791,625, filed Jan. 31, 1997, now abandoned, which is a continuationof U.S. application Ser. No. 08/508,750, filed Jul. 28, 1995, nowabandoned, each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTIONS

1. Field of the Inventions

The inventions generally relate to systems and methods for diagnosing ortreating medical conditions.

2. Description of the Related Art

There are many medical treatments which involve instances of cutting,ablating, coagulating, destroying, or otherwise changing thephysiological properties of tissue (collectively referred to herein as“tissue modification”). For example, tissue modification can be used tochange the electrophysiological properties of tissue. Althoughtreatments that include tissue modification are beneficial, thephysiological changes to the tissue are often irreversible and themodification of tissue other than the intended tissue can disable oreven kill a patient. Accordingly, physicians must carefully select thetissue that is to be treated in this manner.

One area of medical treatment which involves tissue modification is theablation of cardiac tissue to cure various cardiac conditions. Normalsinus rhythm of the heart begins with the sinoatrial node (or “SA node”)generating a depolarization wave front. The impulse causes adjacentmyocardial tissue cells in the atria to depolarize, which in turn causesadjacent myocardial tissue cells to depolarize. The depolarizationpropagates across the atria, causing the atria to contract and emptyblood from the atria into the ventricles. The impulse is next deliveredvia the atrioventricular node (or “AV node”) and the bundle of HIS (or“HIS bundle”) to myocardial tissue cells of the ventricles. Thedepolarization of these cells propagates across the ventricles, causingthe ventricles to contract. This conduction system results in thedescribed, organized sequence of myocardial contraction leading to anormal heartbeat.

Sometimes aberrant conductive pathways develop in heart tissue, whichdisrupt the normal path of depolarization events. For example,anatomical obstacles in the atria or ventricles can disrupt the normalpropagation of electrical impulses. These anatomical obstacles (called“conduction blocks”) can cause the electrical impulse to degenerate intoseveral circular wavelets that circulate about the obstacles. Thesewavelets, called “reentry circuits,” disrupt the normal activation ofthe atria or ventricles. As a further example, localized regions ofischemic myocardial tissue may propagate depolarization events slowerthan normal myocardial tissue. The ischemic region, also called a “slowconduction zone,” creates errant, circular propagation patterns, called“circus motion.” The circus motion also disrupts the normaldepolarization patterns, thereby disrupting the normal contraction ofheart tissue.

The aberrant conductive pathways create abnormal, irregular, andsometimes life-threatening heart rhythms, called arrhythmias. Anarrhythmia can take place in the atria, for example, as in atrialtachycardia (AT), atrial fibrillation (AFIB) or atrial flutter (AF). Thearrhythmia can also take place in the ventricle, for example, as inventricular tachycardia (VT).

In treating VT and certain other arrhythmias, it is essential that thelocation of the sources of the aberrant pathways (called substrates) belocated. Once located, the tissue in the substrates can be destroyed, orablated, by heat, chemicals, or other means of creating a lesion in thetissue. Ablation can remove the aberrant conductive pathway, restoringnormal myocardial contraction. The lesions used to treat VT aretypically relatively deep and have a large surface area. However, thereare some instances where shallower lesions will successfully eliminateVT.

The lesions used to treat AFIB, on the other hand, are typically longand thin and are carefully placed to interrupt the conduction routes ofthe most common reentry circuits. More specifically, the long thinlesions are used to create a maze pattern which creates a convolutedpath for electrical propagation within the left and right atria. Thelesions direct the electrical impulse from the SA node along a specifiedroute through all regions of both atria, causing uniform contractionrequired for normal atrial transport function.

The lesions finally direct the impulse to the AV node to activate theventricles, restoring normal atrioventricular synchrony.

Prior to modifying the electrophysiological properties of cardiac tissueby ablation, or by other means of destroying tissue to create lesions,physicians must carefully determine exactly where the lesions should beplaced. Otherwise, tissue will be unnecessarily destroyed. In addition,the heart is in close proximity to nerves and other nervous tissue andthe destruction of this tissue will result in severe harm to thepatient.

With respect to the treatment of VT, physicians examine the propagationof electrical impulses in heart tissue to locate aberrant conductivepathways. The techniques used to analyze these pathways, commonly called“mapping,” identify regions (or substrates) in the heart tissue whichcan be ablated to treat the arrhythmia. One form of conventional cardiactissue mapping techniques uses multiple electrodes positioned in contactwith epicardial heart tissue to obtain multiple electrograms. Thephysician stimulates myocardial tissue by introducing pacing signals andvisually observes the morphologies of the electrograms recorded duringpacing, which this Specification will refer to as “paced electrograms.”The physician visually compares the patterns of paced electrograms tothose previously recorded during an arrhythmia episode to locate tissueregions appropriate for ablation. These conventional techniques requireinvasive open heart surgical techniques to position the electrodes onthe epicardial surface of the heart.

Conventional epicardial electrogram processing techniques used fordetecting local electrical events in heart tissue are often unable tointerpret electrograms with multiple morphologies. Such electrograms areencountered, for example, when mapping a heart undergoing ventriculartachycardia (VT). For this and other reasons, consistently high correctidentification rates (CIR) cannot be achieved with currentmulti-electrode mapping technologies. In treating VT using conventionalopen-heart procedures, the physician may temporarily render a localizedregion of myocardial tissue electrically unresponsive during an inducedor spontaneous VT episode. This technique, called “stunning,” isaccomplished by cooling the tissue. If stunning the localize regioninterrupts an ongoing VT, or suppresses a subsequent attempt to induceVT, the physician ablates the localized tissue region. However, inconventional practice, cooling a significant volume of tissue to achievea consistent stunning effect is clinically difficult to achieve.

Another form of conventional cardiac tissue mapping technique, calledpace mapping, uses a roving electrode in a heart chamber for pacing theheart at various endocardial locations. In searching for the VTsubstrates, the physician must visually compare all pacedelectrocardiograms (recorded by twelve lead body surfaceelectrocardiograms (ECG's)) to those previously recorded during aninduced VT. The physician must constantly relocate the roving electrodeto a new location to systematically map the endocardium.

These techniques are complicated and time consuming. They requirerepeated manipulation and movement of the pacing electrodes. At the sametime, they require the physician to visually assimilate and interpretthe electrocardiograms. Because the lesions created to treat VTtypically have a large volume, the creation of lesions that areimproperly located results in a large amount of tissue being destroyed,or otherwise modified, unnecessarily. Additionally, because thesetechniques do not distinguish between VTs that require a deep lesion,and VTs that can be treated with a more shallow lesion, tissue will beunnecessarily modified when a deep lesion is made to treat VTs that onlyrequire a more shallow lesion.

Turning to the treatment of AFIB, anatomical methods are used to locatethe areas to be ablated or otherwise modified. In other words, thephysician locates key structures such as the mitral valve annulus andthe pulmonary veins. Lesions are typically formed that blockpropagations near these structures. Additional lesions are then formedwhich connect these lesions and complete the so-called “maze pattern.”However, the exact lesion pattern, and number of lesions created, canvary from patient to patient. This can lead to tissue beingunnecessarily destroyed in patients who need fewer lesions than thetypical maze pattern.

Another issue that often arises in the treatment of AFIB is atrialflutters which remain after the physician finishes the maze procedure.Such flutters are the result of gaps in the lesions that form the mazepattern. The gaps in the lesions must be located so that additionaltissue modification procedures may be performed to fill in the gaps.Present method of locating these gaps are, however, difficult and timeconsuming.

There thus remains a real need for systems and procedures that simplifythe process of locating tissue that is intended for cutting, ablating,coagulating, destroying, or otherwise changing its physiologicalproperties.

SUMMARY OF THE INVENTIONS

One aspect of a present invention provides systems and methods forconducting diagnostic testing of tissue. The systems and methodstransmit an electrical energy pulse that temporarily renders a zone oftissue electrically unresponsive. The systems and methods may also sensean electrophysiological effect due to the transmitted pulse. Based atleast in part upon the sensing of the electrophysiological effect, thephysician can determine whether the temporarily unresponsive tissue isin fact the tissue that is intended for modification. Thus, the presentinvention allows the physician to easily identify the tissue that isintended for modification, as well as tissue that is not.

In the area of cardiac treatment, for example, temporarily renderinglocalized zones of myocardial tissue electrically unresponsive allowsthe physician to locate potential pacemaker sites, slow conduction zonesand other sources of aberrant pathways associated with arrhythmia. Usingthe same process, the physician can selectively alter conductionproperties in the localized zone, without changing electrophysiologicalproperties of tissue outside the zone. With respect to the treatment ofVT, the present invention allows a physician to temporarily create alarge, deep area of electrically unresponsive tissue and then determinewhether such tissue should be made permanently electrically unresponsiveby performing tests which show whether or not the VT has beeneliminated. When treating AFIB, the physician can create continuouslong, thin areas of electrically unresponsive tissue and then performtesting if required to insure that the permanent modification of thetemporarily unresponsive tissue would create the desired therapeuticeffect. Similar techniques may also be used to precisely locate thesources of AF.

Once it is determined that the temporarily unresponsive tissue is thetissue that should be permanently modified to cure the VT, AFIB or otherarrhythmia, the physician can alter an electrophysiological property ofthe myocardial tissue in or near the diagnosed zone. Theelectrophysiological property of myocardial tissue can be altered, forexample, by ablating myocardial tissue in or near the zone. Thephysician will not ablate the tissue if the zone does not meetpreestablished criteria for ablation.

During procedures that are performed in and around neural tissue,physicians can render the tissue temporarily unresponsive prior topermanent modification. Tests can then be performed to determine whetherunwanted paralysis is present. If it is not, the physician can proceedwith modification.

In a preferred embodiment, the systems and methods use radio frequencyenergy to both temporarily render tissue electrically unresponsive aswell as modify the tissue, should the established criteria be met. Thesame electrode (or series of electrodes) may be used to transmit theradio frequency energy, which, in one mode, temporarily renders thetissue electrically unresponsive and which, in a second mode, ablates orotherwise modifies the tissue.

Another one of the present inventions is an electrical energy generatingdevice. A preferred embodiment of the device includes a first elementthat, when activated, generates for transmission by an electrode (orseries of electrodes) coupled to the device an electrical energy pulsethat temporarily renders tissue electrically unresponsive. The devicealso comprises a second element that, when activated, generates fortransmission by an electrode (or series of electrodes) coupled to thedevice electrical energy to modify tissue by, for example, ablating thetissue. A switch may be provided which selects for activation either thefirst element or the second element.

The above described and many other features and attendant advantages ofthe present inventions will become apparent as the invention becomesbetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed description of preferred embodiments of the inventions will bemade with reference to the accompanying drawings.

FIG. 1 is a diagrammatic view of a system for accessing a targetedtissue region in the body for diagnostic or therapeutic purposes inaccordance with one embodiment of a present invention.

FIG. 2 is an enlarged perspective view of a multiple-electrode structurethat may be used in association with the system shown in FIG. 1.

FIG. 3 is an enlarged view of a tissue modification device that may beused in association with the system shown in FIG. 1.

FIG. 4 is a schematic view of a slow conduction zone in myocardialtissue and the circular propagation patterns (called circus motion) itcreates.

FIG. 5 is a diagrammatic view of a representative switching element inaccordance with a preferred embodiment of a present invention that maybe used in association with a radio frequency energy generator to switchbetween a stunning mode and an ablation (or other tissue modification)mode.

FIG. 6 is a perspective view of a flexible probe that includes aplurality of flexible electrodes in accordance with one embodiment of apresent invention.

FIG. 7 is a side view of a flexible probe that includes a flexibleelectrode and a tip electrode in accordance with one embodiment of apresent invention.

FIG. 8 is a side, partial section view of an exemplary flexibleelectrode in accordance with one embodiment of a present invention.

FIG. 9 is a side section view of the interior of the heart with a probein accordance with one embodiment of a present invention positionedtranseptally against the septal wall of the left atrium.

FIG. 10 is an end view of the probe shown in FIG. 9.

FIG. 11 is a side section view of the interior of the heart with theprobe shown in FIG. 9 positioned against the septal wall of the rightatrium.

FIG. 12A is a side view of a probe including a high density array ofelectrodes.

FIG. 12B is a side view of the probe shown in FIG. 12A with the array ofelectrodes in a generally flat orientation.

FIG. 13A is a side view of an exemplary asymmetric electrode supportdevice.

FIG. 13B is an end view of the exemplary asymmetric electrode supportdevice shown in FIG. 13A.

FIG. 14 is a plan view of a system for stunning and/or modifying tissuewhich includes an expandable porous electrode structure in accordancewith one embodiment of a present invention.

FIG. 15 is side view, with portions broken away, of a porous electrodestructure in accordance with one embodiment of a present invention in anexpanded state.

FIG. 16 is side view of the porous electrode structure shown in FIG. 15in a collapsed state.

FIG. 17 is an enlarged side view, with portions broken away, of theporous electrode structure shown in FIG. 15.

FIG. 18 is a side view, with portions broken away, of a porous electrodestructure in accordance with another embodiment of a present invention.

FIG. 19 is side, section view of the porous electrode structure shown inFIG. 18 in a collapsed state.

FIG. 20 is a section view taken generally along line 20—20 in FIG. 17.

FIG. 21 is a side view of a porous electrode structure in accordancewith another embodiment of a present invention.

FIG. 22 is side view, with portions broken away, of a porous electrodestructure in accordance with still another embodiment of a presentinvention.

FIG. 23 is a side view of a surgical device for positioning an operativeelement within a patient in accordance with a preferred embodiment of apresent invention.

FIG. 24 is a side, partial section view of a portion of the surgicaldevice shown in FIG. 23.

FIGS. 25 and 26 are front views of a spline assembly in accordance withone embodiment of a present invention.

FIG. 27 is a partial front, partial section view of a surgical devicefor positioning an operative element within a patient in accordance witha preferred embodiment of a present invention.

FIG. 28 is a side view of a surgical device for positioning an operativeelement within a patient in accordance with another preferred embodimentof a present invention.

FIG. 29 is a side, partial section view of an alternate tip that may beused in conjunction with the device shown in FIG. 28.

FIG. 30 is a section view of the distal portion of the device shown inFIG. 28 taken along line 30—30 in FIG. 28.

FIG. 31 a section view of an alternate distal portion for the deviceshown in FIG. 30.

FIG. 32 is a section view taken along line 32—32 in FIG. 28.

FIG. 33 is a section view showing an electrode coated with regeneratedcellulose.

FIG. 34 is a section view showing a partially masked electrode.

FIG. 35 is a section view showing an alternative electrodeconfiguration.

FIG. 36 is a diagram showing one embodiment of a power supply circuit inaccordance with the present invention.

FIG. 37A is a diagram showing where an additional switching device maybe added to the circuit shown in FIG. 36.

FIG. 37B is a detailed diagram of the switching device shown in FIG.37A.

FIG. 38 is a schematic view of an exemplary graphical userinterface-based system including various diagnostic and therapeuticinstruments.

FIG. 39 is a schematic view of an exemplary graphical userinterface-based system including various diagnostic and therapeuticinstruments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the best presently knownmodes of carrying out the inventions. This description is not to betaken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of the invention.

The detailed description of the preferred embodiments is organized asfollows:

I. Mapping and Stunning-Modification Systems

A. Mapping Devices

B. Process Controller

C. Stunning-Modification Device

D. Power Supply

E. Electrode Selecting Device

F. Graphical User Interface-Based System

II. Additional Devices That May be Used in a Stunning-ModificationSystem

A. Multiple Electrode Stunning-Modification Devices

B. Structures For Positioning Electrodes in a Three-Dimensional Array

C. Expandable-CollapsiblePorous Electrode Structures

D. Surgical Probes

E. Regenerated Cellulose Coating

F. Temperature Sensors

III. Modes of Operation

A. Stunning Mode

B. Power Considerations Associated With Stunning

C. Modification Mode

D. Roving Pacing Mode

E. Electrophysiological Diagnosis Mode

IV. Bypass and Non-Bypass Environment Considerations

The section titles and overall organization of the present detaileddescription are for the purpose of convenience only and are not intendedto limit the present invention.

I. Mapping and Stunning-Modification System

FIG. 1 shows an exemplary system 10 for analyzing endocardial electricalevents, using catheter-based, vascular access techniques in accordancewith one embodiment of a present invention. The system 10 examines thedepolarization of heart tissue that is subject to an arrhythmia andlocates a potential tissue site for ablation or other modification.

The exemplary system 10 shown in FIG. 1 includes a mapping probe 14 anda multi-purpose stunning-modification probe 16. Each probe is separatelyintroduced into the selected heart region 12 through a vein or artery(typically the femoral vein or artery) through suitable percutaneousaccess. The mapping probe 14 and multi-purpose stunning-modificationprobe 16 can be assembled in an integrated structure for simultaneousintroduction and deployment in the heart region 12. Further details ofthe deployment and structures of the probes 14 and 16 are set forth inU.S. Pat. No. 5,636,634, entitled “Systems and Methods Using GuideSheaths for Introducing, Deploying, and Stabilizing Cardiac Mapping andAblation Probes,” which is incorporated herein by reference.

Other types of catheter-based mapping and stunning-modification probesmay also be used. Additionally, the mapping and/or stunning-modificationprobes do not have to be catheter-based and can be in the form of probesthat are inserted into the heart through a thoracotomy, thoracostomy ormedian sternotomy. Examples of such structures are discussed in SectionII-D below.

A. Mapping Devices

Exemplary mapping device 14 has a flexible catheter body 18. The distalend of the catheter body 18 carries a three-dimensionalmultiple-electrode structure 20. In the illustrated embodiment, thestructure 20 takes the form of a basket defining an open interior space22 (see FIG. 2). It should be appreciated that other three-dimensionalstructures could be used.

As FIG. 2 shows, the illustrated basket structure 20 comprises a basemember 26 and an end cap 28. Generally flexible splines 30 extend in acircumferentially spaced relationship between the base member 26 and theend cap 28.

The splines 30 are preferably made of a resilient, biologically inertmaterial, like Nitinol metal or silicone rubber. The splines 30 areconnected between the base member 26 and the end cap 28 in a resilient,pretensed, radially expanded condition, to bend and conform to theendocardial tissue surface they contact. In the illustrated embodiment(see FIG. 2), eight splines 30 form the basket structure 20. Additionalor fewer splines 30 could be used.

The splines 30 carry an array of electrodes 24. In the illustratedembodiment, each spline 30 carries eight electrodes 24. Of course,additional or fewer electrodes 24 can be used.

A slidable sheath 19 is movable along the axis of the catheter body 18(shown by arrows in FIG. 2). Moving the sheath 19 forward causes it tomove over the basket structure 20, collapsing it into a compact, lowprofile condition for introducing into the heart region 12. Moving thesheath 19 rearward frees the basket structure 20, allowing it to springopen and assume the pretensed, radially expanded position shown in FIG.2. The electrodes are urged into contact against the surrounding hearttissue.

Further details of a suitable basket structure are disclosed in U.S.patent application Ser. No. 08/206,414, filed Mar. 4, 1994, and PCTPublication No. WO 9421166, both entitled “Multiple Electrode SupportStructures.”

In use, the electrodes 24 sense electrical events in myocardial tissuefor the creation of electrograms. The electrodes 24 are electricallycoupled to a process controller 32 (see FIG. 1). A signal wire (notshown) is electrically coupled to each electrode 24. The wires extendthrough the body 18 of the device 14 into a handle 21 (see FIG. 2), inwhich they are coupled to an external multiple pin connector 23. Theconnector 23 electrically couples the electrodes to the processcontroller 32.

Alternatively, multiple electrode structures can be located epicardiallyusing a set of catheters individually introduced through the coronaryvasculature (e.g., retrograde through the aorta or coronary sinus), asdisclosed in PCT Publication No. WO 9416619, entitled “MultipleIntravascular Sensing Devices for Electrical Activity.”

B. Process Controller

In the illustrated embodiment, the process controller 32 induceselectrical events in heart tissue by transmitting pacing signals intoheart tissue. The process controller 32 senses these electrical eventsin heart tissue to process and analyze them to locate a potentialablation site.

More particularly (see FIG. 1), the process controller 32 iselectrically coupled by a bus 47 to a pacing module 48, which paces theheart sequentially through individual or pairs of electrodes to inducedepolarization. Details of the process controller 32 and pacing module48 are described in U.S. Pat. No. 5,494,042, entitled “Systems andMethods for Deriving Electrical Characteristics of Cardiac Tissue forOutput in Iso-Characteristic Displays.”

The process controller 32 is also electrically coupled by a bus 49 to asignal processing module 50. The processing module 50 processes cardiacsignals into electrograms. A Model TMS 320C31 processor available fromSpectrum Signal Processing, Inc. can be used for this purpose.

The process controller 32 is further electrically coupled by a bus 51 toa host processor 52, which processes the input from the electrogramprocessing module 50. The output of the host processor 32 can beselectively displayed for viewing by the physician on an associateddisplay device 54. The host processor 32 can be a Pentium™-type or othersuitable microprocessor. The exemplary process controller 32 operates intwo functional modes, called the sampling mode and the matching mode.

Representative matching techniques to find potential ablation sites aredescribed in U.S. patent application Ser. No. 08/390,559, filed Feb. 17,1995, and PCT Publication No. WO 9625094, both entitled “Systems andMethods for Analyzing Biopotential Morphologies in Body Tissue.”

C. Stunning-Modification Device

The exemplary multi-purpose stunning-modification device 16 shown inFIG. 3 includes a flexible catheter body 34 that carries an electrode 36at the distal tip. The electrode is suitable for ablation and othertissue modification procedures. A handle 38 is attached to the proximalend of the catheter body 34. The handle 38 and catheter body 34 carry asteering mechanism 40 for selectively bending or flexing the catheterbody 34 along its length, as the arrows in FIG. 3 show. The steeringmechanism 40 can vary. For example, the steering mechanism can be asshown in U.S. Pat. No. 5,254,088, which is incorporated herein byreference.

A wire (not shown) electrically connected to the electrode 36 extendsthrough the catheter body 34 into the handle 38, where it iselectrically coupled to an external connector 45. The connector 45connects the electrode 36 to a generator 46, which supplieselectromagnetic radio frequency energy to the electrode 36. As used inthis Specification, the term “radio frequency energy” refers toelectrical energy with frequencies in the range of between about 10 kHzto about 3 GHz (3×10⁹ Hz). When operated in a uni-polar mode, anexternal patch electrode (not shown) constitutes the radio frequencyenergy return line. When operated in a bi-polar mode, an electrodecarried on the catheter body 34, or an electrode carried on a nearbycatheter, constitutes the radio frequency energy return line. Thegenerator 46 is operable through an associated switching element 80 intwo modes, called the stunning mode and the modification mode.

D. Power Supply

FIG. 36 illustrates one preferred embodiment of a power supply circuit500 for delivering controlled high voltage RF pulses to tissue. In theexemplary circuit, which is a full-wave bridge rectifier and transformercircuit, a stepped up AC voltage from a variably controllable powersource 502 is rectified into substantially unidirectional (rectified)pulse waveforms for application to body tissue in a safe andcontrollable manner.

The circuit includes a first isolation and step-up transformer T1(preferably having a turns ratio of 10:1) through which power is inputfrom the AC power source 502, and four diodes D1, D2, D3 and D4, withoutput to the input terminal end of a RC circuit. The RC circuit has atleast one shunting capacitor C1, in parallel with resistors R1, R2 andR3 (resistors R1 and R2 are in series with one another and in parallelwith resistor R3). The output terminal end of the RC circuit is thevoltage drop across the capacitor C1. The RC circuit, which alsoincludes switching devices S1 and S2, can be thought of as resonant-typecircuit that stores energy supplied by the AC power supply through thefull-wave bridge rectifier, until such time that the RC circuit isselectively discharged through the primary coils of a second isolationand step-up transformer T2 by operation of switching device S1. Theswitching device S1 connects the transformer T2 with the output voltagedrop at capacitor C1. Output from transformer T2 is applied to a load,which is the body of the patient in the stunning and modificationsystems disclosed herein.

Inputting the AC power from AC power source 502 through the firstisolation and step-up transformer T1 provides at least two advantages.First, it allows the AC source voltage to be stepped up (or steppeddown) as needed. Second, it isolates the AC power source 502 from theremaining circuit, as shown with dashed lines in FIG. 36, therebyreducing the shock hazard to a patient. A similar function is providedby the second step-up and isolation transformer T2. Accordingly, theisolation and step-up transformers T1 and T2 electrically isolate theportion of the circuit circled with dotted lines from the patient andother circuits.

Step-up transformer T2 provides additional safety protection for thepatent, should switching device S1 fail in either the open or closedpositions. If switching device S1 fails in the open position, no poweris delivered, since no current flows through the primary coils oftransformer T2. If the switching device S1 fails in the closed position,substantially rectified voltage waveforms of long duration(predominately DC voltage waveforms) will flow through the primary coilsof transformer T2, and only minor variations in current will bereflected at the secondary coils. Thus, the patient is only exposed toRF pulsed voltage waveforms when S1 is properly working and rapidlybeing switched ON and OFF.

Operation of the exemplary full-wave bridge rectifier shown in FIG. 36allows for substantial rectification of AC waveforms into substantiallyrectified or unidirectional pulsed waveforms (allowing for the usualnon-ideal behavior of actual circuits, ripple voltage, and the like).The secondary voltage of transformer T1, seen at the output oftransformer T1, equals the turns ratio times the primary voltage, e.g.,V_(sec)=(N_(sec)/N_(pri))V_(pri). When the input cycle voltage waveformis positive, diodes D1 and D4 are forward-biased and conduct current inthe direction from node A to node B, and from node D to node C (node Dcan be connected to ground), with the portions of the circuit betweennodes A to D and nodes B to C being an open circuit by nature of diodesD2 and D3 being reverse biased. When the input cycle is negative, diodesD2 and D3 are forward-biased and conduct current in the direction fromnode C to node B and from node D to node A, with the portions of thecircuit between nodes D to C and nodes A to B being an open circuit, bynature of diodes D1 and D4 being reverse biased. A substantiallyfull-wave rectified output voltage appears across node 1 of the circuitand as seen by the RC circuit to the right of node 1.

Diodes D1-D4, which may be Zener diodes, must have reverse breakdownvoltages that exceed the maximum voltage to which the capacitor C1 canbe charged. In one preferred embodiment, the diodes D1-D4 have abreakdown voltage of 300 V, and carry a maximum current flow of lessthan or equal to 0.2 amperes RMS, while capacitor C1 has a value of10,000 μF, and is a high-voltage electrolytic capacitor, such as thekind commonly used for flash cameras. Capacitor C1 can be repeatedlycharged to 350-400 V, and may be connected in parallel with similarcapacitors to achieve the necessary storage capacitance. When charged to300 volts, capacitor C1 stores about 600 J of energy.

The input AC power is preferably about 5 W and 500 W. However, it shouldbe noted that relatively low levels of input power will reduce theoverall flexibility of the system. For example, a 5 W input power sourcewould require at least 2 minutes to fully charge capacitor C1 to thepreferred level of about 600 J. Although a smaller capacitor or lowerstored voltages would enable more rapid charging, the techniquesdisclosed herein require the storage of a significant amount of energyas well as rapid delivery to be effective. With respect to the upperpreferred limit, power levels higher than about 500 W increase thepotential for patient injury in the event of component failure.

The delivered power requirements for stunning targeted tissue using thecircuit shown in FIG. 36 is high. In some instances 800 V must bedelivered into a 50 Ω load, requiring 12 kW of power. As noted inSection III-B with respect to the electrodes used in a three-dimensionalstructure, a RF pulse having an amplitude of 150 volts and a duration ofabout 10 ms will stun tissue to a depth of 5 mm, while a 800 volt RFpulse at 500 kHz frequency and a duration of 10 ms will stun a tissue toa depth of 10 mm. Delivery of this high level of power must be carefullycontrolled, since that level of power can severely injure a patient.

In some special circumstances, voltages as low as 100 V can electricallystun tissue. On the other hand, a short burst of very high voltages(about 4000V) are often required to kill tissue by dielectric breakdownof cell membranes. In order to account for these situations, the voltageoutputs from transformer T1 should range from about 100 V to about 4000V.

In the preferred embodiment, the AC power supply 502 will deliver up to50 W of power and have a maximum peak-to-peak voltage of 30 V, operatingat a frequency of 10-100 kHz. The resistors R1 and R2 may have values of10 kΩ and 100 Ω, respectively, resulting in a decay time constant ofabout 2 minutes and an expected monitoring voltage of 0-3 V across R2.R3 is a power resistor with a resistance value of about 100 Ω, whichenables a more rapid adjustment of the voltage across capacitor C1, suchas when the operator selects a lower stunning voltage. Thus, whenswitching device S2 is closed, the capacitor C1 is discharged, with atime constant of 1.4 sec.

Switching devices S1 and S2 may be switched ON and OFF to produce aplurality of various amplitude and pulse width duration RF pulses.Switching devices S1 and S2 may be any suitable switching device,whether mechanical, electrical or electromechanical, and are preferablysolid state or power semiconductor switches such as an SCR, gateturn-off thyristor (GTO), power MOSFET, transistor, thyristor, or hybriddevices with FET input and a bipolar output stage. The switching devicesS1 are S2 are preferably controlled by a processor 504 (which may bepart of process controller 32 shown in FIG. 1 or a separate component),and/or with suitable computation circuits, where applicable, to producein conjunction with the circuit shown in FIG. 36 a plurality or train ofwaveform pulses of RF frequency at the output 2—2 of the circuit. Thesevoltage pulses are stepped up by transformer T2, having a turns ratio of4:1, for application to the patient.

Shunting resistors R1 and R2 can serve two purposes. First, when the ACpower from power supply 502 is shut off, the resistors drain charge andreduce power from capacitor C1. Second, the voltage across resistor R2is measured by the controller 504 and is used to control the AC powersupply 502. The AC power supply can be controlled by the controller 504to vary its output power and frequency.

To further provide for isolation, the voltage measurement of resistor R2by controller 504 may be made by optical isolation, or other isolationmeasuring techniques such as magnetic isolation or telemetry.

The circuit of FIG. 36 controls the cycle length of the rectified RFpulse, the amplitude of the pulse, and the total duration of the pulsethorough selective discharge of the capacitor through the selectiveswitching of the switching device S2, which discharges the capacitorthrough shunting resistor R3, and selective switching of switchingdevice S1, which creates a plurality of rectified RF pulse waveformsthat feed through step-up transformer T2. This produces a RF voltagepulse train for application to the tissue in the patient's body. Theduty cycle of the RF voltage pulse train may also be controlled by theselective switching ON and OFF of switching device S1. The centerfrequency for the pulse waveform is preferably between about 100 kHz and1 MHz, with the waveform generated using ON/OFF duty cycles of from 10%to 50%. Frequencies above about 100 Mhz are not effective in a voltagestunning mode because dielectric absorption results in high heatingrates in the tissue, while frequencies below about 100 kHz can directlystimulate tissue, which is not desirable.

In one preferred embodiment, the switching device S1 is turned ON andOFF with a cycle length of 2 μsec and a duty cycle of 50%, for a totalpulse duration of 10 ms. To produce this pulse train, a train of 5,0001.0 μsec long pulses turn switching device S1 to the ON state, to createa 10 msec long 500 kHz pulse waveform at the output 2-2 of FIG. 36,which are then suitably stepped up in voltage in a 4:1 ratio bytransformer T2 for output to the tissue.

The rectified AC waveform produced by turning switching device S1 ON andOFF at a 500 kHz repetition rate would, in the absence of filtering,produce a nearly square wave. However, finite switching times for theswitching device S1 and the transformer T2, which acts as a bandpassfilter, strongly filter out the higher harmonics of the base frequencyof the pulse waveform, resulting in a stunning waveform as applied totissue that can be made to be somewhat sinusoidal. Should a more perfectsinusoidal waveform be desired, using the teachings of the presentinvention one could produce a more perfect sinusoidal waveform by thetuning of the output transformer T2 to the center frequency of the pulsewaveform used to stun tissue.

Energy outputted to the patient can be reduced by limiting the powerprovided by the AC power supply 502 and the energy stored in capacitorC1. For one preferred embodiment of the invention, stored energy at thecapacitor C1 is 600 J and the AC power supply used to charge C1 islimited to 50 W. Under maximum transfer rates, C1 is discharged with atime constant of 77 msec. After several hundred msec, C1 is largelydischarged, and the power delivery rate will drop to less than 30 W.Plateau power delivery rates to the patient are decreased from 50 W atthe AC power supply input to 30 W at the output due to power losses,such as losses in transformers T1 and T2.

It should be noted that the exemplary power supply circuit issusceptible to many variations. The only requirement is that power besupplied to a storage device and discharged from the storage device byway of a switching device that produces the desired pulses. For example,should it be found that their functionality is not required in aparticular application, the resistors in the RC circuit could beeliminated. Storage devices other than capacitors may be employed. TheAC power supply and rectifier arrangement illustrated in FIG. 36 may bereplaced by a battery (or plurality of batteries in series) and asuitable ON/OFF switch. Also, the transformer T2 can be replaced byanother type of inductive device.

E. Electrode Selecting Device

As discussed in Section III-A, a sequence of stunning pulses can beapplied with different electrodes in a multiple electrode structure(such as those discussed in Section II and shown in FIGS. 10-13B) tocreate a complex pattern of temporarily unresponsive tissue. One exampleof an electrode selecting device that may be used to switch from one (ormore) electrodes to another (or more) electrodes in, for example thecircuit shown in FIG. 36, is shown in FIGS. 37A and 37B. Exemplaryswitching device S3 includes a plurality of mechanical orelectromechanical switches SW₁-SW_(N). Preferably, each switchSW₁-SW_(N) is associated with an individual electrode E₁-E_(N). Thus,the state of the switch SW determines whether the associated electrodewill deliver the stunning voltage.

Relay or mechanical switches are preferred because these switches canhave very low coupling capacitances across the switch, as compared tosingle solid state power switches. The switches should normally be openin order to promote patient safety and minimize the switching powerrequirements.

Should relatively fast switching times be desired, four or more switcheswith relatively low ON resistances could be used in series, therebydecreasing the effective capacitance across the switch. Here, the switchSW may be formed from multiple solid state switches in series. It shouldbe noted, however, that such an arrangement will greatly complicate theswitch drive circuitry.

F. Graphical User Interface-Based System

One example of a graphical user interface-based system that may be usedto sequentially apply either a single high voltage pulse or a series ofhigh voltage pulses to tissue is illustrated in FIGS. 38 and 39. In theillustrated embodiment, the system 310 includes an instrument 312 (suchas a catheter or surgical probe) having an array of electrodes 318, aswell as instruments 314 and 316, which include operative elements usablefor diagnostic or therapeutic purposes. One exemplary operative elementis a device for imaging body tissue, such as an ultrasound transducer oran array of ultrasound transducers, an optic fiber element, or a CT orMRI scanner. Other exemplary operative elements include device todeliver drugs or therapeutic material to body tissue, or electrodes forsensing a physiological characteristic in tissue or transmitting energyto stimulate or ablate tissue.

The exemplary system 310 includes one or more instrument controllers(designated 320, 322, and 324) which, in use, condition the associatedinstrument 312, 314, and 316 to perform its respective diagnostic ortherapeutic function. To aid in coordinating signal and data flow amongthe controllers 320, 322, and 324 and their linked instruments, thesystem 310 includes an interface 326 (or “master switching unit) thatestablishes electrical flow paths and processes the various diagnosticor therapeutic data and signals in an organized and efficient fashion. Asuitable interface is disclosed in U.S. application Ser. No. 08/770,971,entitled “Unified Switching System for Electrophysiological Stimulationand Signal Recording and Analysis,” filed Dec. 12, 1996, andincorporated herein by reference.

The exemplary system 310 also includes a main processing unit (MPU) 328,which is preferably a Pentium™ microprocessor. The MPU 328 includes aninput/output (I/O) device 330, which controls and monitors signal anddata flow to and from the MPU 328. The I/O device 330 can, for example,consist of one or more parallel port links and one or more conventionalserial RS-232C port links or Ethernetm communication links. The I/Odevice 330 is coupled to a data storage module or hard drive 332, aswell as to the instrument interface 326 and a printer 334. An operatorinterface module 336, which is coupled to the I/O device 330, includes agraphics display monitor 338, a keyboard input 340, and a pointing inputdevice 342, such as a mouse or trackball. The graphics display monitor338 can also provide for touch screen (finger or stylus) input. Anoperating system 344 for the MPU 328 may, for example, reside as processsoftware on the hard drive 332, which is down loaded to the MPU 328during system initialization and startup. In the illustrated embodiment,the operating system 344 executes through the operator interface 336 agraphical user interface (GUI) 346.

The operating system 344 administers the activation of a library 348 ofcontrol applications, which are designated, for purpose of illustration,as A1 to A7 in FIG. 38. In the illustrated embodiment, the controlapplications A1 to A7 all reside in storage 354 as process software onthe hard drive 332 and are down loaded and run based upon operator inputthrough the GUI 346. Each control application A1 to A7 prescribesprocedures for carrying out given functional tasks. Of course, thenumber and functions of the applications A1 to A7 can vary. Exemplaryfunctions include clinical procedures, specialized navigationapplications, and utility applications.

Clinical procedure applications contain the steps to carry out aprescribed clinical procedure, such as the sequential application ofstunning pulses to predetermined electrodes in a two orthree-dimensional array. A number of such applications may be stored,each corresponding to an area, or areas, of stunned tissue havingvarious shapes and sizes. That way, the physician need only select thedesired shape with the GUI 346 to form the desired area of temporarilyunresponsive tissue. Similar application programs may be used to formareas of permanently unresponsive tissue using the high voltagepulse-based modification techniques described in Section III-C below.

The navigation applications allow the operator to visualize on the GUI346 the orientation of the multiple electrode array 312 and instruments314 and 316, thereby assisting the operator in manipulating andpositioning the array and instruments. For example, one navigationapplication may construct an ideal or virtual image of the deployedarray and the instruments, while the other displays an actual, real-timeimage of each.

Utility applications carry out system testing, system servicing,printing, and other system support functions affecting the applications.

When run by the operating system 344, each application generatesprescribed command signals, which the I/O device 330 distributes via theinstrument interface 326 to condition the instrument controllers 320,322, and 324 to perform a desired task using the instruments 312, 314,and 316. The I/O device 326 also receives data from the instrumentcontrollers 320, 322, and 324 via the instrument interface 326 forprocessing by the procedure application being run. The GUI 346 presentsto the operator, in a graphical format, various outputs generated by theprocedure application run by the operating system 344 and allows theuser to alter or modify specified processing parameters in real time.

The operating system 344 also includes one or more specialty functions(designated F1 and F2 in FIG. 38), which run in the background duringexecution of the various applications A1 to A7. For example, onefunction F1 can serve to establish and maintain an event log 350 whichkeeps time track of specified important system events as they occurduring the course of a procedure. Another function F2 can serve toenable the operator, using the GUI 346, to down load patient specificinformation generated by the various applications A1 to A7 to the harddrive 332 as data base items, for storage, processing, and retrieval,thereby making possible the establishment and maintenance of a patientdata base 352 for the system 310.

As illustrated in FIG. 39, the exemplary multiple electrode array is athree-dimensional basket structure 358 carried at the distal end 356 ofa catheter or surgical probe. The exemplary basket structure includeseight spaced apart spline elements (alphabetically designated A to H inFIG. 39) assembled together by a distal hub 360 and a proximal base 362.Each spline carries eight electrodes which are numerically designated oneach spline from the most proximal to the most distal electrode as 1 to8. The basket structure 358 thus supports a total of sixty-fourelectrodes. Of course, a greater or lesser number of spline elementsand/or electrodes can be present. Each of the electrodes is electricallyconnected to an individual conductor in a multiple conductor cable 364.The splines can either be arranged symmetrically, as shown in FIG. 39,or asymmetrically as shown in FIGS. 13A and 13B to provide a highdensity electrode array. A stunning energy source 380 can also becoupled to the electrodes, either through the instrument interface 326(as shown in solid lines in FIG. 39), or through its own instrumentinterface 326″ (shown in phantom lines in FIG. 39) coupled to the MPU328.

Instrument 314 may be carried at the distal end 366 of a catheter orsurgical probe. In the illustrated embodiment, instrument 314 includesan electrode 368 for sensing electrical activity in tissue, as well asto transmitting energy to stimulate or ablate tissue. The electrode 368is electrically connected by a cable 370 to the instrument interface326. A generator 378 for transmitting radio frequency ablation energycan also be coupled to the electrode 368, either through the instrumentinterface 326 (as shown in solid lines in FIG. 39), or through its owninstrument interface 326′ (shown in phantom lines in FIG. 39) coupled tothe MPU 328. Instrument 316, which may be carried at the distal end of acatheter or surgical probe, includes an imaging device 372 whichoperates using a visualizing technique such as fluoroscopy, ultrasound,CT, or MRI, to create a real-time image of a body region. A cable 376conveys signals from the imaging device 372 to the instrument interface326.

Clinical procedure applications can also be designed and implementedduring a procedure using the GUI 346. Based on the images provided bythe navigation applications of the electrode support structure, thephysician can select the electrodes that will produce the desired area,or areas, of permanently or temporarily unresponsive tissue. The imageof the electrode support structure will preferably appear as it does inFIG. 39, i.e. with the spline letters and electrodes numbers visible.The desired electrodes can be selected using the keypad by typing thespline element letters and electrode number. For example, A5, B5 and C5can be selected to produce an area which spans spline elements, or A3,A4 and A5 can be selected to produce an area which extends along asingle spline element. Alternatively, the electrodes may be selected byway of the touch screen or pointing device.

Unless otherwise desired, the pulses will occur in the order that theelectrodes are selected. Other information, such as pulse length, timebetween pulses, pulse magnitude, etc. can also be input via the GUI 346.Instead of delivering energy sequentially, the system can be configuredsuch that a plurality of electrodes transmit energy simultaneously. Suchsimultaneous transmission may be part of a sequence that includes otherelectrodes transmitting energy simultaneously or individually. Thisfeature may also be selected on the GUI 346.

Additional information concerning the GUI-based system illustrated inFIGS. 38 and 39 may be found in U.S. application Ser. No. 09/048,629,entitled “Interactive Systems and Methods For Controlling the Use ofDiagnostic or Therapeutic Instruments in Interior Body Regions,” filedMar. 26, 1998, and incorporated herein by reference.

II. Additional Devices That May be Used in a Stunning-ModificationSystem

A. Multiple Electrode Stunning-Modification Probes

Probe configurations employing multiple electrodes may also be used toform continuous, elongate areas of modified or temporarily electricallyunresponsive (i.e. “stunned”) tissue. Such areas may be either straightor curvilinear. Examples of such multiple electrode probes are shown inU.S. Pat. Nos. 5,545,193 and 5,582,609, both of which are incorporatedherein by reference.

As shown by way of example in FIG. 6, an exemplary multiple elementprobe 100 includes a plurality of segmented, generally flexibleelectrodes 102 carried on a flexible body 104. The flexible body 104 ismade of a polymeric, electrically nonconductive material, likepolyethylene or polyurethane, and preferably carries within it aresilient bendable wire or spring with attached steering wires so it canbe flexed to assume various curvilinear shapes. The electrodes 102 arepreferably spaced apart lengths of closely wound, spiral coils made ofelectrically conducting material, like copper alloy, platinum, orstainless steel. The electrically conducting material can be coated withplatinum-iridium or gold to improve its conduction properties,radiopacity and biocompatibility. Instead of a single length of woundwire, one or more of the electrodes 102 may be formed from multiple,counter wound layers of wire. The electrodes may also be formed from ahypotube that is machined into a coil. Additionally, the other electrodestructures disclosed in the present specification may also be used incombination with this embodiment.

Alternatively, a ribbon of electrically conductive material can bewrapped about the flexible body 104 to form a flexible electrode.Flexible electrodes may also be applied on the flexible body by coatingthe body with a conductive material, like platinum-iridium or gold,using conventional coating techniques or an ion beam assisted deposition(IBAD) process. For better adherence, an undercoating of nickel ortitanium can be applied.

In another preferred embodiment, and as shown by way of example in FIG.7, a generally rigid tip electrode 106 may be combined with thegenerally flexible electrodes. Of course, the tip electrode 106 could bea generally flexible electrode structure made of a closely wound coil orother flexible material. Temperature sensing elements 298, such asthermocouples or thermistors, may also be provided. Temperature sensingis discussed in detail in Section II-F below.

The flexible body 104 can be remotely steered to flex it into a desiredshape, or it can possess a preformed shape. In the latter situation,removing a constraint (such as a sheath, not shown), enables theoperator to change the segment from straight to curvilinear. The probebody may also be formed from a malleable material, which is especiallyuseful when the probe is part of a surgical probe that is notcatheter-based. Such probes are discussed in Section II-D below.

The number of electrodes and the spacing between them, can vary,according to the particular objectives of the therapeutic procedure. Forexample, the probe shown in FIG. 6 is well suited for creatingcontinuous, elongated lesion patterns (or patterns of tissue modified inother ways) as well as continuous, elongated areas of stunned tissue,provided that the electrodes are adjacently spaced close enough togetherto create additive heating/stunning effects when energy is transmittedsimultaneously to the adjacent electrodes. The additive heating effectsbetween close, adjacent electrodes intensifies the desired effect on thetissue contacted by the electrodes. The additive heating effects occurwhen the electrodes are operated simultaneously in a bipolar modebetween electrodes or when the electrodes are operated simultaneously ina unipolar mode, transmitting energy to an indifferent electrode.

More particularly, when the spacing between the electrodes is equal toor less than about 3 times the smaller of the diameters of theelectrodes, the simultaneous emission of energy by the electrodescreates an elongated continuous lesion pattern, or area of stunnedtissue, in the contacted tissue area due to the additive effects.Similar effects are obtained when the spacing between the electrodes isequal to or less than about 2 times the longest of the lengths of theelectrodes.

To consistently form long, thin, continuous curvilinear lesion patternsor areas of electrically unresponsive tissue, additional spatialrelationships among the electrodes must be observed. When the length ofeach electrode is equal to or less than about 5 times the diameter ofthe respective electrode, the curvilinear path that the probe takesshould create a distance across the contacted tissue area that isgreater than about 8 times the smaller of the diameters of theelectrodes. The simultaneous application of energy will form acontinuous elongate lesion pattern, or area of stunned tissue, thatfollows the curved periphery contacted by the probe, but does not spanacross the contacted tissue area. The same effect will be obtained whenthe length of each electrode is greater than about 5 times the diameterof the respective electrode, and the curvilinear path that supportelement takes should create a radius of curvature that is greater thanabout 4 times the smallest the electrode diameters. Of course, thespacing between the electrodes must be such that additive heatingeffects are created.

Taking the above considerations into account, it has been found thatadjacent electrode segments having lengths of less than about 2 mm donot consistently form the desired continuous lesions. Such constraintsdo not apply to areas of stunned tissue. Techniques to stun tissue to 5mm to 10 mm in depth using small electrodes are discussed in SectionIII-B. For ablation purposes, flexible electrode elements can range from2 mm to 50 mm in length and are preferably 12.5 mm in length with 2 to 3mm spacing. The diameter of the electrodes and underlying flexible bodycan vary from about 4 French to about 10 French in catheter-type probes.The tip electrode is preferably from 4 mm to 10 mm in length.

The flexibility of the coil electrodes can be increased by spacing theindividual coil windings, which increases the ability of the windings toclosely conform to irregular anatomical surfaces. The windings ofelectrodes should be spread apart by a distance that is at least ⅕ ofthe width of the material that makes up the individual coils.Preferably, the distance is ½ of the width. Referring to FIG. 8, thedistance D can also vary along the length of the electrode. Here, theelectrode 110 includes a first zone 112 of windings that are spacedapart and two second zones 114 of windings that are closely adjacent toone another. The closely spaced zones provide a support structure fortemperature sensing elements, which as discussed below in Section II-F,may be advantageously placed at the longitudinal ends of the electrode.Although the exemplary electrode shown in FIG. 8 has a rectangularcross-section, other configurations, such as a round cross-section, canalso be employed.

Power can be supplied to the electrodes individually or, as describedabove, the power can be simultaneously supplied to more than one or evenall of the electrodes. The supply of power to the electrodes can becontrolled in the manner disclosed in U.S. Pat. No. 5,545,193.

B. Structures For Positioning Electrodes in a Three-Dimensional Array

There are many instances where it is advantageous to position electrodesin a three-dimensional array. For example, the interatrial septum(identified by the letter S in FIG. 9) has been shown to be a junctionfor the propagation of atrial fibrillation wavelets. FIGS. 9 and 10 showa device 116 adapted to locate multiple electrodes 118 against a largearea of the interatrial septum (S). The device 116 may be used in thesame manner as the mapping device 14 shown in FIG. 2. The device mayalso be used to deliver RF energy to ablate tissue. For example, asubset of the electrodes on the array can be used to simultaneouslydeliver RF energy to the tissue contacting the electrodes. The subset ischosen based on the geometry and dimensions of the region to be ablated.The region may be a long, continuous line used to treat AFIB, a largecircular area used to treat the subendocardial substrates that cause VT,or any other geometry necessary to ablate the substrate(s) causing aparticular physiologic event.

Although device 116 is shown as part of a catheter-based device, it mayalso be employed in a surgical probe that is not catheter-based. Suchprobes are discussed in Section II-D below.

The device 116 includes an array of spline elements 120 that radiate ina star-like pattern from the distal end 122 of a catheter tube 124 (asthe end view in FIG. 10 best shows). Each spline element 120 carriesmultiple electrodes 118. As shown by way of example in FIG. 9, thecatheter tube 124 is deployed through a conventional transeptal sheath126 into the left atrium. During introduction, the sheath 126 enclosesthe device 116, maintaining the device in a collapsed condition. Oncelocated in the left atrium, the sheath 126 is pulled back past theseptum S, and the spline elements 120, freed of the sheath 126, springopen. The physician pulls the catheter tube 124 back to bring theelectrodes 118 into contact against the septal wall within the leftatrium.

Turning to FIG. 11, the device 116 can be deployed in the right atriumby introduction through the sheath 126. Retraction of the sheath 126allows the spline elements 120 to spring open. The physician pushes thecatheter tube 124 toward the septum S to place the electrodes 118 intocontact against the septal wall within the right atrium.

Another device, generally represented by reference numeral 128 in FIGS.12A and 12B, includes a high density array of electrodes 130 that can beplaced against the septal wall in the right atrium, or against anotherregion anywhere within the heart. The device 128 includes an array ofspline elements 132 constrained between a proximal anchor 134 and adistal hub 136. The device 128 is attached to the distal end 138 of acatheter tube 140. However, it may also be employed in a surgical probethat is not catheter-based.

The spline elements 132 carry the electrodes 130 such that they areconcentrated in a high density pattern about the distal hub 136. Awayfrom the distal hub 136, the spline elements 132 are free of electrodes130.

A stylet 142 extends through the catheter tube bore 144 and is attachedat its distal end to the distal hub 136. The proximal end of the stylet142 is attached to a push-pull control mechanism 146 in the cathetertube handle 148. As FIG. 12B shows, pulling back on the mechanism 146(arrow 147) draws the distal hub 136 toward the proximal anchor 134. Thedistal region of the spline elements 132 bend and deform outward, toform a generally planar surface 150 radiating about the distal hub 136,on which the electrodes 130 are located. The surface 150 presents thehigh density pattern of electrodes 130 for intimate surface contact witha large region of heart tissue. The distal hub 136 can be made of anenergy transmitting material and serve as an electrode to increase theelectrode density.

FIGS. 13A and 13B show another example of a device (or “supportassembly”) that may be used to position a high density array ofelectrodes against a bodily structure. The support assembly 129 can beattached to the distal end of a catheter or surgical probe and includesan array of flexible spline elements 131 extending longitudinallybetween a distal hub 133 and a base 135. The geometry of the assembly129 is asymmetric in a radial sense. That is, when viewed from distalhub 133, as FIG. 13B shows, the spline elements 131 do not radiate fromthe main axis at generally equal circumferential intervals. Instead,there are at least some adjacent spline elements 131 that arecircumferentially spaced apart more than other adjacent spline elements131. The largest angle measured between two adjacent spline elements inthe assembly (designated angle α in FIG. 13B) preferably exceeds thesmallest angle measured between two other adjacent spline elements(designated angle β in FIG. 13B).

Due to the radial asymmetry of the assembly 129, not all the splineelements 131 need to carry electrodes 137. The geometry of the assembly129 is symmetric in an axial sense. The proximal region 139 and thedistal region 141 of each spline are, or capable of being, occupied byelectrodes 137.

The exemplary embodiment shown in FIGS. 13A and 13B includes ten splineelements 131, designated S1 to S10. The exemplary asymmetric arrangementincludes a first discrete group 145 of five adjacent spline elements 131(S1 to S5) and a second discrete group 149 (S6 to S10). The groups 145and 149 are shown to be diametrically arranged, and each group 145 and149 occupies an arc of about 90°. Within each group, the adjacent splineelements S1 to S5 and S6 to S10 are circumferentially spaced apart inequal intervals of about 22° (which comprises angle β). However, thespline elements S1/S10 and S5/S6, marking the boundaries between thegroups 145 and 149, are circumferentially spaced farther apart, at about90° (which comprises angle α). This non-uniform circumferential spacingof the spline elements 131 exemplifies one type of radially asymmetricstructure.

Preferably, the distance between electrode s on different splineelements within a group of spline elements (such as S1 to S5) is equalto the distance between electrodes on a spline element within the group.In other words, the distance between two adjacent electrodes on a splineelement is the same as the distance between two adjacent electrodesrespectively located on adjacent spline elements. Such an arrangementsimplifies the process of forming complex two-dimensional patterns (orlarge areas) of stunned or permanently modified tissue.

Other types of asymmetric structures for positioning electrodes in athree-dimensional array, such as axially asymmetric structures, aredisclosed in U.S. patent application Ser. No. 08/742,569, entitled“Asymmetric Multiple Electrode Support Structures,” filed Oct. 28, 1996,which is incorporated herein by reference.

C. Expandable-Collapsible Porous Electrode Structures

Device configurations employing expandable-collapsible porous electrodestructures can be used to form areas of modified or temporarilyunresponsive tissue that are either large and deep, small and shallow,or large and shallow. Examples of such devices are shown in FIGS. 15-22.These devices may be used in the same manner as the device shown inFIGS. 1 and 3. Additionally, although the devices shown in FIGS. 15-22are part of catheter-based devices (such as that shown in FIG. 14), thefeatures of the devices may be employed in surgical probes that are notcatheter-based. Such probes are discussed in Section II-D below.

Additional information concerning expandable-collapsible porouselectrode structures, which are preferably formed from regeneratedcellulose, can be found in U.S. patent application Ser. No. 08/631,575,entitled “Tissue Heating and Ablation Systems and Methods Using PorousElectrode Structures,” which is incorporated herein by reference.

1. Expandable-Collapsible Porous Electrode Structure Configurations

FIG. 14 shows a tissue modification-stunning system 152 that includes aflexible catheter tube 154 with a proximal end 156 and a distal end 158.The proximal end 156 carries a handle 160. The distal end 158 carries anelectrode structure 162. As shown by way of example in FIGS. 15 and 20,the electrode structure 162 includes an expandable-collapsible body 164.The geometry of the body 164 can be altered between a collapsed geometry(FIG. 16) and an enlarged, or expanded, geometry (FIG. 15). In theillustrated embodiments, liquid pressure is used to inflate and maintainthe expandable-collapsible body 164 in the expanded geometry.

As illustrated for example in FIGS. 14-16, the catheter tube 154 carriesan interior lumen 166 along its length. The distal end of the lumen 166opens into the hollow interior of the expandable-collapsible body 164.The proximal end of the lumen 166 communicates with a port 168 on thehandle 160. The liquid inflation medium 170 is conveyed under positivepressure through the port 168 and into the lumen 166. The liquid medium170 fills the interior of the expandable-collapsible body 164. Theliquid medium 170 exerts interior pressure to urge theexpandable-collapsible body 164 from its collapsed geometry to theenlarged geometry.

This characteristic allows the expandable-collapsible body 164 to assumea collapsed, low profile (ideally, less than 8 French diameter, i.e.,less than about 0.267 cm) when introduced into the vasculature. Oncelocated in the desired position, the expandable-collapsible body 164 canbe urged into a significantly expanded geometry of, for example,approximately 5 mm to 20 mm. Expandable-collapsible bodies with largerprofiles may be used in conjunction with probes that are notcatheter-based.

As shown by way of example in FIGS. 18 and 19, the structure 162 caninclude, if desired, a normally open, yet collapsible, interior supportstructure 172 to apply internal force to augment or replace the force ofliquid medium pressure to maintain the body 164 in the expandedgeometry. The form of the interior support structure 172 can vary. Itcan, for example, comprise an assemblage of flexible spline elements174, as shown in FIG. 18, or an interior porous, interwoven mesh or anopen porous foam structure.

The exemplary internally supported expandable-collapsible body 164 isbrought to a collapsed geometry, after the removal of the inflationmedium, by outside compression applied by an outer sheath 178 (see FIG.19), which slides along the catheter tube 154. Forward movement of thesheath 178 advances it over the expanded expandable-collapsible body164. The expandable-collapsible body 164 collapses into its low profilegeometry within the sheath 178. Rearward movement of the sheath 178retracts it away from the expandable-collapsible body 164. Free from theconfines of the sheath 178, the interior support structure 172 springsopen to return the expandable-collapsible body 164 to its expandedgeometry to receive the liquid medium.

As illustrated for example in FIG. 18, the structure 162 furtherincludes an interior electrode 180 formed of an electrically conductivematerial carried within the interior of the body 164. The material ofthe interior electrode 180 has both a relatively high electricalconductivity and a relatively high thermal conductivity. Materialspossessing these characteristics include gold, platinum,platinum/iridium, among others. Noble metals are preferred. An insulatedsignal wire 182 is coupled to the electrode 180. The signal wire 182extends from the electrode 180, through the catheter tube 154, to anexternal connector 185 on the handle 160. The connector 185 electricallycouples the electrode 180 to a radio frequency generator.

In accordance with the exemplary embodiments, the liquid medium 170 usedto fill the body 164 includes an electrically conductive liquid. Theliquid 170 establishes an electrically conductive path, which conveysradio frequency energy from the electrode 180. In conjunction, the body164 comprises an electrically non-conductive thermoplastic orelastomeric material that contains pores 184 on at least a portion ofits surface. The pores 184 of the body 164 (shown diagrammatically inenlarged form for the purpose of illustration) establishes ionictransport of the tissue stunning or modification energy from theelectrode 180, through the electrically conductive medium 170, to tissueoutside the body. Preferably, the liquid 170 possesses a low resistivityto decrease ohmic loses, and thus ohmic heating effects, within the body164. In the illustrated and preferred embodiment, the liquid 170 alsoserves the additional function as the inflation medium for the body, atleast in part.

The composition of the electrically conductive liquid 170 can vary. Inthe illustrated and preferred embodiment, the liquid 170 comprises ahypertonic saline solution, having a sodium chloride concentration at ornear saturation, which is about 20% weight by volume. Hypertonic salinesolution has a low resistivity of only about 5 ohm.cm, compared to bloodresistivity of about 150 ohm.cm and myocardial tissue resistivity ofabout 500 ohm.cm. Alternatively, the composition of the electricallyconductive liquid medium 170 can comprise a hypertonic potassiumchloride solution. This medium, while promoting the desired ionictransfer, requires closer monitoring of rate at which ionic transportoccurs through the pores 184, to prevent potassium overload. Whenhypertonic potassium chloride solution is used, it is preferred keep theionic transport rate below about 1 mEq/min.

Due largely to mass concentration differentials across the pores 184,ions in the medium 170 will pass into the pores 184, because ofconcentration differential-driven diffusion. Ion diffusion through thepores 184 will continue as long as a concentration gradient ismaintained across the body 164. The ions contained in the pores 184provide the means to conduct current across the body 164.

When radio frequency energy is conveyed from a generator to theelectrode 180, electric current is carried by the ions within the pores184. The RF currents provided by the ions result in no net diffusion ofions, as would occur if a DC voltage were applied, although the ions domove slightly back and forth during the RF frequency application. Thisionic movement (and current flow) in response to the applied RF fielddoes not require perfusion of liquid in the medium 170 through the pores184. The ions convey radio frequency energy through the pores 184 intotissue to a return electrode, which is typically an external patchelectrode (forming a unipolar arrangement). Alternatively, thetransmitted energy can pass through tissue to an adjacent electrode(forming a bipolar arrangement). The radio frequency energy may be usedto heat tissue (mostly ohmically) to form a lesion, or to render tissuetemporarily unresponsive.

The preferred geometry of the expandable-collapsible body is essentiallyspherical and symmetric, with a distal spherical contour. However,nonsymmetric or nonspherical geometries can be used. For example, theexpandable-collapsible body may be formed with a flattened distalcontour, which gradually curves or necks inwardly for attachment withthe catheter tube. Elongated, cylindrical geometries can also be used.

The exemplary segmented porous zones 198 shown in FIG. 21 are wellsuited for use in association with folding expandable-collapsible bodies164. In this arrangement, the regions that are free of pores comprisecreased or folding regions 204. It should be appreciated that thefoldable body 164 shown in FIG. 21 can also be used for other patternsof porous regions. The creased regions 204 can also be provided withpores, if desired.

2. Pore Patterns

The pattern of pores 184 that define the porous region of the body mayvary. As shown by way of example in FIGS. 15 and 16, the region of atleast the proximal ⅓ surface of the expandable-collapsible body 164 isfree of pores 184 and the porous region is in the form of a continuouscap on the distal ⅓ to ½ of the body. This configuration is useful whenit is expected that ablation will occur with the distal region of body164 oriented in end-on contact with tissue. Alternatively, theelectrically conductive porous region may be segmented into separateenergy transmission zones arranged in a concentric “bulls eye” patternabout the distal tip of the body 164. When it is expected that tissuestunning or modification will occur with the side region of the body 164oriented in contact with tissue, the porous region is preferablysegmented into axially elongated energy transmission zones, which arecircumferentially spaced about the body.

3. Non-porous Conductive and Marking Regions

FIG. 22 shows an embodiment of an expandable-collapsible electrodestructure 206 that includes one or more nonporous, electricallyconductive regions 208 on the surface of the body 164. In theillustrated embodiment, the nonporous conductive regions 208 comprisemetal, such as gold, platinum, platinum/iridium, among others, depositedupon the expandable-collapsible body 164 by sputtering, vapordeposition, ion beam deposition, electroplating over a deposited seedlayer, or a combination of these processes. Alternatively, the nonporousconductive regions 208 can comprise thin foil affixed to the surface ofthe body. Still alternatively, the nonporous conductive regions cancomprise solid fixtures carried by the porous body 164 at or morelocations. Signal wires (not shown) within the body are electricallycoupled to the nonporous regions. The signal wires traverse the cathetertube 154 for coupling to the connectors 185 carried by the handle 160.

Various ways for attaching nonporous electrodes 208 and associatedsignal wires to an expandable-collapsible electrode body 164 aredescribed in U.S. patent application Ser. No. 08/629,363, entitled“Enhanced Electrical Connections for Electrode Structures,” which isincorporated herein by reference.

The nonporous regions 208 can be used to sense electrical activity inmyocardial tissue. The sensed electrical activity is conveyed to anexternal controller, which processes the potentials for analysis by thephysician. The processing can create a map of electrical potentials ordepolarization events for the purpose of locating potential arrhythmiasubstrates. Once located with the nonporous regions 208, the porousregions 198 can be used to convey radio frequency energy as previouslydescribed to ablate the substrates. Alternatively, or in combinationwith sensing electrical activities, the nonporous regions 208 can beused to convey pacing signals. In this way, the nonporous regions cancarry out pace mapping or entrainment mapping.

Opaque markers may be deposited on the interior surface of the body 164so that the physician can guide the device under fluoroscopy to thetargeted site. Any high-atomic weight material is suitable for thispurpose. For example, platinum, platinum-iridium. can be used to buildthe markers. Preferred placements of these markers are at the distal tipand center of the structure 164.

The expandable-collapsible structure 206 shown in FIG. 22 therebycombines the use of “solid” nonporous electrodes 208 with “liquid” orporous electrodes 198. The expandable-collapsible structure makespossible the mapping of myocardial tissue for therapeutic purposes usingone electrode function, and the stunning or modification of tissue fortherapeutic purposes using a different electrode function.

4. Electrical Resistivity of the Expandable-Collapsible Body

The electrical resistivity of the body 164 has a significant influenceon the lesion geometry and controllability. It has been discovered thatablation with devices that have a low-resistivity body 164 (below about500 ohm.cm) requires more RF power and results in deeper lesions. On theother hand, devices that have a high-resistivity body 164 (at or aboveabout 500 ohm.cm) generate more uniform heating, therefore, improve thecontrollability of the lesion. Because of the additional heat generatedby the increased body resistivity, less RF power is required to reachsimilar tissue temperatures after the same interval of time.Consequently, lesions generated with high-resistivity bodies 164 usuallyhave smaller depth. The electrical resistivity of the body 164 can becontrolled by specifying the pore size of the material, the porosity ofthe material, and the water adsorption characteristics (hydrophilicversus hydrophobic) of the material. A detailed discussion of thesecharacteristics, as well as the formation of the expandable-collapsiblebody, can be found in the aforementioned U.S. application Ser. No.08/631,575, entitled “Tissue heating and Ablation Systems and MethodsUsing Porous Electrode Structures.”

Generally speaking, pore diameters smaller than about 0.1 μm retainmacromolecules, but allow ionic transfer through the pores in responseto the applied RF field. With smaller pore diameters, pressure drivenliquid perfusion through the pores 184 is less likely to accompany theionic transport, unless relatively high pressure conditions developwithin the body 164. Larger pore diameters (less than 8 μm) prevent mostblood cells from crossing the membrane, but permit passage of ions inresponse to the applied RF field. With larger pore diameters, pressuredriven liquid perfusion, and the attendant transport of macromoleculesthrough the pores 184, is also more likely to occur at normal inflationpressures for the body 164.

Low or essentially no liquid perfusion through the pores 184 ispreferred because it limits salt or water overloading, caused bytransport of the hypertonic solution into the blood pool and it allowsionic transport to occur without disruption. When undisturbed byattendant liquid perfusion, ionic transport creates a continuous virtualelectrode 186 (see FIG. 20) at the body 164-tissue interface. Thevirtual electrode 186 efficiently transfers RF energy without need foran electrically conductive metal surface.

With respect to porosity, the placement of the pores 184 and the size ofthe pores 184 determine the porosity of the body 164. The porosityrepresents the space on the body 164 that does not contain material, oris empty, or is composed of pores 184. Expressed as a percentage,porosity represents the percent volume of the body 164 that is notoccupied by the body material. The magnitude of the porosity affects theliquid flow resistance of the body 164, as discussed above. Theequivalent electrical resistivity of the body 164 also depends on itsporosity. Low-porosity materials have high electrical resistivity,whereas high-porosity materials have low electrical resistivity. Forexample, a material with 3% porosity, when exposed to 9% hypertonicsolution (resistivity of 5 ohm.cm), may have an electrical resistivitycomparable to that of blood or tissue (between 150 and 450 ohm.cm).

For a given a porosity value, an array of numerous smaller pores 184 istypically preferred, instead of an array of fewer but larger pores,because the presence of numerous small pores 184 distributes currentdensity so that the current density at each pore 184 is less. Withcurrent density lessened, the ionic flow of electrical energy to tissueoccurs with minimal diminution due to resistive heat loss. An array ofnumerous smaller pores 184 is also preferred because it further helps toimpose favorably large liquid flow resistance. It is also preferablethat the porous body 164 possess consistent pore size and porositythroughout the desired ablation region to avoid localized regions ofhigher current density and the formation of lesions that are nottherapeutic because they do not extend to the desired depth or length.

A dynamic change in resistance across a body 164 can be brought about bychanging the diameter of the body 164 made from a porous elasticmaterial, such as silicone. In this arrangement, the elastic body 164 ismade porous by drilling pores of the same size in the elastic materialwhen in a relaxed state, creating a given porosity. As the elastic body164 is inflated, its porosity remains essentially constant, but the wallthickness of the body 164 will decrease. Thus, with increasing diameterof the body 164, the resistance across the body 164 decreases, due todecreasing wall thickness and increasing surface area of the body 164.The desired lesion geometry may be specified according to the geometryof the body 164. This enables use of the same porous body 164 to formsmall lesions, shallow and wide lesions, or wide and deep lesions, bycontrolling the geometry of the body 164.

Turning to water absorption characteristics, hydrophilic materials aregenerally preferable because they possess a greater capacity to provideionic transfer of RF energy without significant liquid flow through thematerial.

D. Surgical Probes

As noted above, the present inventions are not limited to catheter-baseddevices and may be incorporated into surgical probes which are notcatheter-based. Such probes allow the physician to directly apply theelectrode or other operative element to tissue. Additional informationconcerning such probes, and uses thereof, may be found in U.S. patentapplication Ser. No. 08/949,117, entitled “Systems and Methods forPositioning a Diagnostic or Therapeutic Element Within the Body,” whichis incorporated herein by reference.

As illustrated for example in FIGS. 23 and 24, a surgical device (or“probe”) 210 for positioning an operative element 214 within a patientincludes a relatively short shaft 216 and a substantially triangularlyshaped spline assembly 234. The relatively short shaft may be betweenapproximately 4 and 18 inches in length, and is preferably 8 inches inlong, while the outer diameter of the shaft is preferably betweenapproximately 6 and 24 French. The operative element preferably consistsof a plurality of electrode elements 250. The spline assembly 234consists of first and second side legs 236 and 238 and a distal leg 240.The distal leg 240, which is preferably non-linear from end to end andapproximately 10 to 12 cm in length, includes first and second linearportions 242 and 244 and a bent portion 246 located mid-way between theends. This spline configuration provides a spring force against theselected bodily surface during use (such as the atrium wall in a cardiacprocedure) and the bend in the distal leg 240 optimizes the contactbetween the operative element 214 and the selected surface. The surgicalprobe 210 also includes a first handle 228 and a second handle 229.

The spline assembly 234 will collapse in the manner shown in FIG. 24when a tubular member 226 (such as a sheath) is advanced thereover andwill return to the orientation shown in FIG. 23 when the tubular memberis retracted. The tubular member 226 preferably includes a raisedgripping surface 230.

During use of the exemplary surgical device shown in FIGS. 23 and 24,the handle 229 is grasped by the physician and force is applied throughthe shaft 216 and side legs 236 and 238 to the operative elementsupporting distal leg 240. The shaft 216 and side legs 236 and 238 maybe configured such that they collapse and form a semicircle with thedistal leg 240 when force is applied to the shaft. Here, the operativeelement should be appropriately masked in one of the manners describedbelow to limit contact of the operative element to the intended bodilystructure.

The exemplary embodiment illustrated in FIGS. 23 and 24 may also beprovided without the tubular member 226. Such devices are especiallyuseful in surgical procedures associated with a thoracotomy or a mediansternotomy, where the spline assemblies can be easily collapsed andadvanced to the desired location, or advanced into the desired locationwithout being collapsed. Here, the spline assemblies can be malleable,if desired, as opposed to simply being bendable.

The spline assemblies illustrated in FIGS. 23 and 24 are preferably madefrom resilient, inert wire, like nickel titanium (commercially availableas Nitinol material) or 17-7 stainless steel. However, resilientinjection molded inert plastic can also be used. The wire or moldedplastic is covered by suitable biocompatible thermoplastic orelastomeric material such as PEBAX® or pellethane. Preferably, thevarious portions of the spline assemblies comprises a thin, rectilinearstrips of resilient metal or plastic material. Still, othercross-sectional and longitudinal configurations can be used. Forexample, the spline legs can decrease in cross-sectional area in adistal direction, by varying, e.g., thickness or width or diameter (ifround), to provide variable stiffness along its length. Variablestiffness can also be imparted by composition changes in materials or bydifferent material processing techniques. The distal leg 240 may beconfigured such that the leg is flat at the distal end, but becomes moresemicircular in cross-section as the leg becomes more proximal in orderto taper the stiffness profile and prevent lateral movement of thespline assembly. The curvature of the spline legs may also be varied andthe lateral ends of the distal leg may be reinforced in order to providemore lateral stability.

As shown by way of example in FIGS. 25-27, the spline assembly of theprobe shown in FIGS. 23 and 24 may be replaced by a curved splineassembly 252. Here, the spline assembly includes a flat, inert wire 254(preferably formed from Nitinol) that acts as a spring and an outerportion 256 (preferably formed from PEBAX® or pellethane). Viewed incross-section, the flat wire 254 has a long side and a short side. Assuch, the spline assembly 252 will deflect in the manner shown in FIG.26 when “in plane” forces F are applied to the spline assembly.Conversely, the assembly will resist bending when “out of plane” forcesare applied. As such, it may be used to form an arcuate lesion during,for example, a procedure where a lesion is formed around the pulmonaryvein.

It should be noted here that the wire 254 does not have to berectangular in cross-section. Other cross-sectional shapes where thelength is greater than the width can also be used. The wire 254 can alsobe made from a malleable material such as partially or fully annealedstainless steel instead of the spring-like material discussed above. Themalleable embodiments will enable the operator to form fit the ablationelement support structure to irregular anatomical structures.

As shown in FIG. 27, exemplary spline assembly 252 may include first andsecond steering wires 251 a and 251 b that are secured to thespring-like flat wire 254 by, for example, welding or adhesive bonding.The proximal ends of the steering wires 251 a and 251 b are operablyconnected to a knob 255 on a handle 248 by way of a cam (not shown). Thehandle 248 also includes provisions for the steering wires 251 a and 251b. Rotation of the knob 255 will cause the spline assembly to move sideto side. Thus, in addition to simply moving the handle, the physicianwill be able to move the operative element 214 within the patient byrotating the knob 255. Such movement is useful when the physician isattempting to precisely locate the operative element within the patientand/or control the contact force between the operative element and thetissue surface. This is especially true when the handle and or shaft 216cannot be moved, due to anatomical or surgical constraints.

In the exemplary embodiment shown in FIG. 27, the steering wires 251 aand 251 b are both secured at about the midpoint of the flat wire loop.Other configurations are possible depending on the configuration of theloop that is desired after the knob 255 is rotated. For example, onewire could be secured closer to the top of the loop than the other. Theshape of the cam may also be varied. More detailed discussions of theuse of steering wires, albeit in conventional catheter settings, can befound in commonly assigned U.S. Pat. Nos. 5,195,968, 5,257,451, and5,582,609, which are incorporated herein by reference.

The shaft 216 is preferably relatively stiff. As used herein the phrase“relatively stiff” means that the shaft (or other structural element) iseither rigid, malleable, or somewhat flexible. A rigid shaft cannot bebent. A malleable shaft is a shaft that can be readily bent by thephysician to a desired shape, without springing back when released, sothat it will remain in that shape during the surgical procedure. Thus,the stiffness of a malleable shaft must be low enough to allow the shaftto be bent, but high enough to resist bending when the forces associatedwith a surgical procedure are applied to the shaft. A somewhat flexibleshaft will bend and spring back when released. However, the forcerequired to bend the shaft must be substantial. Rigid and somewhatflexible shafts are preferably formed from stainless steel, whilemalleable shafts are formed from annealed stainless steel.

One method of quantifying the flexibility of a shaft, be it shafts inaccordance with the present invention or the shafts of conventionalcatheters, is to look at the deflection of the shaft when one end isfixed in cantilever fashion and a force normal to the longitudinal axisof the shaft is applied somewhere between the ends. Such deflection (σ)is expressed as follows:

σ=WX ²(3L−X)/6EI

where:

W is the force applied normal to the longitudinal axis of the shaft,

L is the length of the shaft,

X is the distance between the fixed end of the shaft and the appliedforce,

E is the modulous of elasticity, and

I is the moment of inertia of the shaft.

When the force is applied to the free end of the shaft, deflection canbe expressed as follows:

σ=WL ³/3EI

Assuming that W and L are equal when comparing different shafts, therespective E and I values will determine how much the shafts will bend.In other words, the stiffness of a shaft is a function of the product ofE and I. This product is referred to herein as the “bending modulus.” Eis a property of the material that forms the shaft, while I is afunction of shaft geometry, wall thickness, etc. Therefore, a shaftformed from relatively soft material can have the same bending modulusas a shaft formed from relatively hard material, if the moment ofinertia of the softer shaft is sufficiently greater than that of theharder shaft.

For example, a relatively stiff 2 inch shaft (either malleable orsomewhat flexible) would have a bending modulus of at leastapproximately 1 lb.-in.² Preferably, a relatively stiff 2 inch shaftwill have a bending modulus of between approximately 3 lb.-in.² andapproximately 50 lb.-in.². By comparison, 2 inch piece of a conventionalcatheter shaft, which must be flexible enough to travel through veins,typically has bending modulus between approximately 0.1 lb.-in.² andapproximately 0.3 lb.-in.². It should be noted that the bending modulusranges discussed here are primarily associated with initial deflection.In other words, the bending modulus ranges are based on the amount offorce, applied at and normal to the free of the longitudinal axis of theshaft, that is needed to produce 1 inch of deflection from an at rest(or no deflection) position.

As noted above, the deflection of a shaft depends on the composition ofthe shaft as well as its moment of inertia. The shaft could be made ofelastic material, plastic material, elasto-plastic material or acombination thereof. By designing the shaft 216 to be relatively stiff(and preferably malleable), the surgical tool is better adapted to theconstraints encountered during the surgical procedure. The forcerequired to bend a relatively stiff 2 inch long shaft should be in therange of approximately 1.5 lbs. to approximately 12 lbs. By comparison,the force required to bend a 2 inch piece of conventional catheter shaftshould be between approximately 0.2 lb. to 0.25 lb. Again, such forcevalues concern the amount of force, applied at and normal to the free ofthe longitudinal axis of the shaft, that is needed to produce 1 inch ofdeflection from an at rest (or no deflection) position.

Ductile materials are preferable in many applications because suchmaterials can deform plastically before failure due to fracturing.Materials are classified as either ductile or brittle, based upon thepercentage of elongation when the fracture occurs. A material with morethan 5 percent elongation prior to fracture is generally consideredductile, while a material with less than 5 percent elongation prior tofracture is generally considered brittle. Material ductility can bebased on a comparison of the cross sectional area at fracture relativeto the original cross area. This characteristic is not dependent on theelastic properties of the material.

Alternatively, the shaft could be a mechanical component similar toshielded (metal spiral wind jacket) conduit or flexible Loc-Line®, whichis a linear set of interlocking ball and socket linkages that can have acenter lumen. These would be hinge-like segmented sections linearlyassembled to make the shaft.

The exemplary tubular member 226 illustrated in FIGS. 23 and 24 ispreferably in the form of a relatively thin cylindrical sheath (e.g.,with a wall thickness of about 0.005 inch) and has an outer diameterwhich is preferably less than 0.180 inch. The sheath material ispreferably also lubricious, to reduce friction during movement of thesheath relative to the shaft 216 and spline assembly 234. For example,materials made from polytetrafluoroethylene (PTFE) can be used for thesheath. The distal end of the sheath should be relatively flexible toprevent injury. If necessary, additional stiffness can be imparted tothe remaining portion of the sheath by lining the sheath with a braidedmaterial coated with PEBAX® material (comprising polyethel block amiderelated to nylon). Other compositions made from PTFE braided with astiff outer layer and other lubricious materials can be used.

Alternatively, the tubular member 226 may be relatively stiff and formedfrom the materials described above with respect to the shaft 216.

As shown by way of example in FIG. 28, a surgical probe 260 inaccordance with another embodiment of a present invention includes arelatively stiff shaft 262, a handle 264 and a distal section 266. Theshaft 262 consists of a hypotube 268, which is either rigid orrelatively stiff, and an outer polymer tubing 270 over the hypotube. Arelatively stiff tube, either malleable or somewhat flexible, willpreferably have a bending modulus of between approximately 3 lb.-in.²and approximately 50 lb.-in.². The handle 264 is similar to the handle228 discussed above in that it includes a PC board 272 for connectingthe operative elements on the distal portion of the probe to a powersource. The handle 264 preferably consists of two molded handle halvesand is also provided with strain relief element 274. An operativeelement 214 (here, in the form of a plurality of electrode elements 54)is provided on the distal section 266. This embodiment is particularlyuseful because it can be easily inserted into the patient through anintroducing port such as a trocar.

In those instances where a malleable shaft 262 is desired, the hypotube268 may be the heat treated malleable hypotube 268 shown in FIGS. 28 and32. By selectively heat treating certain portions of the hypotube, onesection of the hypotube (preferably the distal section) can be made moremalleable than the other. This will alleviate any discontinuity betweenthe distal section 266 and the shaft 262 when the distal section ismalleable.

The distal section 266 can be either somewhat flexible, in that it willconform to a surface against which it is pressed and then spring back toits original shape when removed from the surface or, as noted above,malleable. A bending modulus of between 3 lb.-in.² and 50 lb.-n.² ispreferred. As shown by way of example in FIG. 30, a somewhat flexibledistal section 266 may include a spring member 280, which is preferablyeither a solid flat wire spring (as shown) or a three leaf flat wireNitinol spring, that is connected to the distal end of the hypotube 268.Other spring members, formed from materials such as 17-7 or carpenter'ssteel, may also be used. A series of lead wires 282 and 284 connect theelectrode elements 250 and temperature sensor elements (discussedbelow), respectively, to the PC board 272. The spring member 280 andleads wires 282 and 284 are enclosed in a flexible body 286, preferablyformed from PEBAX® material, polyurethane, or other suitable materials.The spring member 280 may also be pre-stressed so that the distal tip ispre-bent in the manner shown in FIG. 28. Also, an insulating sleeve 281may be placed between the spring member 280 and the lead wires 282 and284.

In those instances where a malleable distal section 266 is desired, thespring member 280 may be replaced by a mandrel 287 made of suitablymalleable material such as annealed stainless steel or beryllium copper,as illustrated for example in FIG. 31. The mandrel will ideally be fixedto the distal tip of the device (by, for example, soldering, spotwelding or adhesives) and run through the shaft into the handle where itwill also be fixed to insure good torque transmission and stability ofthe distal tip. Alternatively, the malleable mandrel may be fixeddirectly within the distal end of the shaft's hypotube 268 and securedby, for example, soldering, spot welding or adhesives.

The distal section 266 may also be formed by a hypotube that is simply acontinuation of the shaft hypotube 268. However, the distal end hypotubecan be a separate element connected to the shaft hypotube 268, if it isdesired that the distal end hypotube have different stiffness (orbending) properties than the shaft hypotube.

The shaft 262 may be from 4 inches to 18 inches in length and ispreferably 6 to 8 inches. The distal section 266 may be from 1 inch to10 inches in length and is preferably 2 to 3 inches. The length of theelectrode elements may range from approximately 4 mm to approximately 20mm. To facilitate the formation of long continuous lesions or areas ortemporarily unresponsive tissue, the distal section 266 preferablyincludes six electrode elements 250 that are approximately 12 mm inlength and approximately 2 to 3 mm apart. This aspect of the inventionsis discussed in Section II-A above with reference to FIGS. 6-8. Thenumber and length of the electrode elements 250 can, of course, bevaried to suit particular applications.

In accordance with some embodiments of the invention, and as shown byway of example in FIG. 29, the distal section 266 may be provided with adistal (or tip) electrode. The distal electrode 276 may be a solidelectrode with a through hole for one or more temperature sensors.Distal electrodes have a variety of applications. For example, a distalelectrode may be dragged along an anatomical surface to create a longlesion. The distal electrode may also be used to touch up lesions orareas of unresponsive tissue (straight or curvilinear) created byelectrode elements 250 if, for example, the distal section 266 does notexactly conform to the anatomical surface, and to continue lesions andareas of temporarily unresponsive tissue formed by the electrodeelements. The distal electrode may also be used to create lesions andareas of temporarily unresponsive tissue in anatomical ridges that areshaped such that the integrity of the surgical device would becompromised if the distal section 266 were bent to conform to the ridge.

In the exemplary embodiments illustrated in FIGS. 23-35, the operativeelement 214 is made up of a plurality of electrode elements 250 whichcan serve a variety of different purposes. The operative elements mayalso be devices such as lumens for chemical ablation, laser arrays,ultrasonic transducers, microwave electrodes, and D.C. hot wires. Suchdevices may also be incorporated into the other embodiments disclosed inthe present specification as appropriate.

In the illustrated embodiments, the principal use of the electrodeelements 250 is to transmit electrical energy and, more particularly, RFenergy, to modify or stun heart and other tissue. However, the electrodeelements 250 can also be used to sense electrical events in heart andother tissue. Alternatively, or in addition, the electrode elements 250can serve to transmit electrical pulses to measure the impedance ofheart tissue, to pace heart tissue, or to assess tissue contact.

The electrode elements 250 are electrically coupled to individual wires(see reference numeral 288 FIG. 35 and reference numeral 282 in FIGS. 30and 31) to conduct energy to them. The wires are passed in conventionalfashion through a lumen extending through one of the spline legs and theshaft 216 into a PC board in the handle, where they are electricallycoupled to a connector which is received in a port in the handle. Theconnector can be used to plug into a source of energy, such as RFablation or tissue stunning, energy. A plurality of temperature sensingelements (not shown), such as theremocouples or thermistors, may also beprovided on the spline assemblies shown herein. Such temperature sensingelements may be located on, under, abutting the edges of, or in between,the electrode elements 250. The temperature sensing elements, and theplacement thereof, is discussed in detail below in Section II-F. Fortemperature control purposes, signals from the temperature sensorelements are transmitted to the source of energy by way of wires (seereference numeral 294 FIG. 35 and reference numeral 284 in FIGS. 30 and31) which are also connected to the PC board. The respective numbers ofwires will, of course, depend on the numbers of sensors and electrodesused in a particular application.

The electrode elements 250, as well as the other electrodes discussed inthe present specification, can be assembled in various ways. They can,for example, comprise multiple, generally rigid electrode elementsarranged in a spaced apart, segmented relationship. The segmentedelectrodes can each comprise solid rings of conductive material, likeplatinum, which makes an interference fit about the annular splinemember. Alternatively, the electrode segments can comprise a conductivematerial, like platinum-iridium or gold, coated upon the device usingconventional coating techniques or an ion beam assisted deposition(IBAD) process. The electrodes can also be in the form of helicalribbons.

Alternatively, the electrode elements 250, as well as the otherelectrodes discussed in the present specification, can comprise spacedapart lengths of closely wound, spiral coils wrapped on the device whichform an array of generally flexible electrode elements, as discussed inSection II-A above with reference to FIGS. 6-8. The coils are made ofelectrically conducting material, like copper alloy, platinum, orstainless steel, or compositions such as drawn-filled tubing (e.g. acopper core with a platinum jacket). The electrically conductingmaterial of the coils can be further coated with platinum-iridium orgold to improve its conduction properties and biocompatibility.

Electrode elements 250, as well as the other electrodes discussed in thepresent specification, can be formed with a conductive ink compound thatis pad printed onto a non-conductive tubular body. A preferredconductive ink compound is a silver-based flexible adhesive conductiveink (polyurethane binder), however other metal-based adhesive conductiveinks such as platinum-based, gold-based, copper-based, etc., may also beused to form electrodes. Such inks are more flexible than epoxy-basedinks.

E. Regenerated Cellulose Coating

As illustrated for example in FIG. 33, the electrode elements 250, aswell as the other electrodes disclosed in the present specification, caninclude a porous material coating 296, which transmits ablation energythrough an electrified ionic medium. For example, as disclosed in U.S.patent application Ser. No. 08/879,343, filed Jun. 20, 1997, entitled“Surface Coatings For Catheters, Direct Contacting Diagnostic andTherapeutic Devices,” which is incorporated herein by reference,electrode elements and temperature sensor elements may be coated withregenerated cellulose, hydrogel or plastic having electricallyconductive components. With respect to regenerated cellulose, thecoating acts as a mechanical barrier between the surgical devicecomponents, such as electrodes, preventing ingress of blood cells,infectious agents, such as viruses and bacteria, and large biologicalmolecules such as proteins, while providing electrical contact to thehuman body. The regenerated cellulose coating also acts as abiocompatible barrier between the device components and the human body,whereby the components can now be made from materials that are somewhattoxic (such as silver or copper).

For applications in which the ablation electrode is in contact withflowing blood as well as tissue, such as when the patient is not onbypass, coating electrodes with regenerated cellulose decreases theeffect of convective cooling on the electrode because regeneratedcellulose is a poor thermal conductor as compared to metal. Thus, theeffect of convective cooling by blood flowing past the regeneratedcellulose coated electrodes is diminished. This provides better controlfor a lesion-generating process because the hottest tissue temperatureis closer to the ablation electrode.

Furthermore, the regenerated cellulose coating decreases the edgeeffects attributed to delivering RF energy to an electrode having asharp transition between the conductive electrode and insulatingmaterial. The current density along the electrode and power densitywithin tissue are more uniform, which reduces the incidence and severityof char and/or coagulum formation. The more uniform current densityalong the axis of the device also results in a more uniform temperaturedistribution at the electrode, which decreases the requirement forprecise placements of the temperature sensors at the ablationelectrodes. Additionally, by coating a device with regenerated celluloseto create the outer surface, less labor-intensive methods of formingelectrodes and bonding wires to electrode surfaces can be used.

F. Temperature Control

Temperature sensing elements 298, such as thermistors or thermocouples,may be used in conjunction with any of the electrodes (or otheroperative elements) disclosed in the present specification. Preferably,the temperature sensing elements 298 are located at the side edges ofthe electrodes where the electrodes abut the underlying,non-electrically conductive support body, such as the support body 104shown in FIGS. 6 and 8 or the polymer outer tubing 270 shown in FIG. 28.RF current densities are high at the edges because the edges are regionswhere electrical conductivity is discontinuous. The resultant rise incurrent density at the electrode edges generates localized regions ofincreased power density and, therefore, regions where highertemperatures exist. Nevertheless, the temperature sensing elements mayalso be located on, under, or in between, the electrode elements in anyof the exemplary devices disclosed herein.

In the preferred embodiment illustrated in FIG. 8, a thin strip ofelectrically insulating material 295 (such as an electricallynon-conducting adhesive) is applied to the support body near the closelyspaced regions in order to minimize the presence of edge currenteffects. Additionally, the temperature sensing elements can be mountedeither on the inside surface of the electrodes or on the outside surfaceencapsulated in an epoxy or PTFE coating 297.

As illustrated for example in FIG. 15, the porous electrode structure162 can carry one or more temperature sensing elements 298. The sensingelements 298 are in thermal conductive contact with the exterior of theelectrode structure 162 to sense conditions in tissue outside thestructure 162. Temperatures sensed by the temperature sensing elements298 are processed by a controller. Based upon temperature input, thecontroller adjusts the time and power level of radio frequency energytransmissions by the electrode 180, to achieve the desired therapeuticobjectives. Various ways for attaching temperature sensing elements toan expandable-collapsible electrode body are described in U.S. patentapplication Ser. No. 08/629,363, entitled “Enhanced ElectricalConnections for Electrode Structures,” which is incorporated herein byreference.

Additionally, a reference temperature sensing element may be provided.For example, a reference temperature sensing element 299 may be providedon or near the distal tip of the device shown in FIG. 28. The referencetemperature sensor may, alternatively, be located in the handle so thatroom temperature will be used as the reference. Another alternative isto use an electronic circuit to function as the reference temperaturesensor. A reference temperature sensor can also be placed on the patientor in the operating room and the physician can simply input thereference temperature into the power control device. It should be notedthat the accuracy of the reference temperature sensor is less importantin applications where the patient is on bypass because the convectivecooling effects of blood flowing past the electrodes is substantiallyreduced. Also, the present surgical devices provide better tissuecontact than conventional catheter-based devices, which provides moreaccurate temperature monitoring.

Suitable power controllers which control power to an electrode based ona sensed temperature are disclosed in U.S. Pat. Nos. 5,456,682 and5,582,609, and the aforementioned U.S. patent application Ser. No.08/949,117, each of which are incorporated herein by reference.

III. Modes of Operation

The operating modes are discussed in the context of cardiac treatment.Nevertheless, and as noted above, the present inventions may be used totreat other types of tissue.

A. Stunning Mode

Referring to FIGS. 1 and 5, in the stunning (or first) mode, thegenerator 46 transmits via the switching element 80 one or more highvoltage pulses through one or more of the electrode(s) discussed aboveinto a local tissue region contacting or otherwise near theelectrode(s). Operation of the switching element 80 is discussed inSection III-C. The electrode configuration may be in the form of asingle electrode, a series of spaced electrodes, or anexpandable-collapsible electrode structure. Thus, references to“electrode(s)” in this section are references to all of the electrodeconfigurations disclosed in the present specification. Each pulse has aprescribed waveform shape and duration that temporarily “stuns” tissuein the local region without field stimulating tissue in regions fartheraway from the electrode(s). The temporary stunning creates a likewisetemporary electrical conduction block in the local region, rendering thetissue region electrically unresponsive to spontaneous or induceddepolarization events. By observing the effect of the local conductionblock upon ongoing cardiac events, the physician obtains diagnosticinformation helpful in locating and confirming potential tissuemodification sites.

By purposeful operation of the electrode(s) in the stunning mode inregions where the process controller 32 has assigned a potentialablation site, the system 10 is able to confirm and cross-check thelocation output of the process controller 32 to verify the location of apotentially efficacious modification site before actually modifyingtissue.

By way of example, the site appropriate for ablation to cure VTtypically constitutes a slow conduction zone, designated SCZ in FIG. 4.Depolarization wave fronts (designated DWF in FIG. 4) entering the slowconduction zone SCZ (at site A in FIG. 4) break into errant, circularpropagation patterns (designated B and C in FIG. 4), called “circusmotion.” The circus motions disrupt the normal depolarization patterns,thereby disrupting the normal contraction of heart tissue to cause thecardiac event.

The event-specific templates T(i) generated by the process controller 32record these disrupted depolarization patterns. When a pacing signal isapplied to a slow conduction zone, the pacing signal gets caught in thesame circus motion (i.e., paths B and C in FIG. 4) that triggers thetargeted cardiac event. A large proportion of the associated pacingmorphologies P(i) at the sensing electrodes E(i) will therefore matchthe morphologies recorded during the targeted cardiac event.

However, when a pacing signal is applied outside a slow conduction zone,the pacing signal does not get caught in the same circus motion. Itpropagates free of circus motion to induce a significantly differentpropagation pattern than the one recorded during the targeted cardiacevent. A large proportion of the pacing morphologies P(i) at the sensingelectrodes E(i) therefore do not match those recorded during thetargeted cardiac event. The difference in propagation patterns betweenpacing inside and outside a slow conduction zone is particularlypronounced during entrainment pacing. For this reason, entrainmentpacing is preferred.

Ablating or otherwise modifying tissue in or close to the slowconduction zone (designated SCZ in FIG. 4) prevents subsequentdepolarization. The destroyed tissue is thereby “closed” as a possiblepath of propagation. Depolarization events bypass the ablated region andno longer become caught in circus motion. In this way, ablation canrestore normal heart function in the treatment of VT. In treating VT,the physician therefore places the electrode(s) in a located tissueregion where the process controller 32 identifies potential efficaciousablation site. The process controller 32 can include a homing module 70to aid the physician in guiding the electrode(s) in the located region.Systems and methods for operating the homing module 70 are disclosed inU.S. Pat. No. 5,722,402, and entitled “Systems and Methods for GuidingMovable Electrode Elements Within Multiple Electrode Structures”, whichis incorporated herein by reference.

With the electrode(s) in position, and before transmitting ablationenergy, the physician conditions the generator 46 through the switchingelement 80 for operation in the stunning mode. The physician alsoconditions the process controller 32 to induce the cardiac event to betreated, which in this example is VT, unless the cardiac event isotherwise spontaneously occurring. As the cardiac event occurs, theelectrode(s) transmits one or more stunning pulses into the tissueregion nearest to it. The stunning pulses are timed to the localelectrogram to be transmitted when local depolarization occurs.

When the selected pulse stuns tissue laying in the modification-targetedzone, the temporarily rendering of this zone electrically unresponsivewill temporarily interrupt the cardiac episode, just as ablation in thezone will permanently stop the cardiac episode. In this respect,stunning serves as a temporary preview of the intended permanentmodification.

Should the stunning interrupt the cardiac episode, the physician waitsfor the temporary conduction block to resolve. Typically, this will takeabout 30 seconds. When a cardiac episode is interrupted, somearrhythmias will not spontaneously recur immediately after the temporaryconduction block has resolved. Here, the episode must be re-induced byconventional programmed stimulation, burst pacing, or other inductionmethods. After the physician confirms the similarity of the episode tothe previous targeted event, the physician may repeat the transmissionof one or more stunning pulses to confirm the interruption of theepisode. Such a procedure confirms that the substrate which is causingthe event, and which is targeted for ablation, is near the electrode(s).

If the episode continues uninterrupted despite the transmission of oneor more stunning pulses, the physician knows that the stunned tissuedoes not include the targeted slow conduction zone. In thiscircumstance, the physician repositions the electrode(s) to a differentlocation geometrically near to the last stunned site. The physiciantransmits one or more stunning pulses into tissue at the new site andobserves the effect upon the spontaneous or induced episode.

The physician repeats these steps, operating the electrode(s) in thestunning mode in the vicinity of all tissue regions the processcontroller 34 assigns a potential ablation site, until a site wherestunning consistently interrupts the arrhythmia or other condition islocated.

When the stunning pulse or pulses repeatedly interrupt the spontaneousor induced episode at a given site, the physician targets the site forablation. The physician can titrate the volume of tissue comprising theslow conduction zone by varying the amplitude of the stunning pulse andobserving the effect. Having targeted the modification site and titratedits volume, the physician, without altering the position of theelectrode(s), conditions the generator 46 through the switching element80 for operation in the modification mode.

As noted above, some cases of VT can be cured with lesions that aresomewhat shallower than those typically used to cure VT. In accordancewith a present invention, the electrode(s) can be used to stun tissue toa relatively shallow depth. A relatively shallow lesion will be createdif the relatively shallow area of unresponsive tissue prevents VT.Otherwise, progressively deeper areas of tissue can be stunned andtested until the VT is eliminated. This way, the depth of thepermanently modified tissue will be no greater than necessary.

Another method of identifying appropriate ablation sites in the VTtreatment context involves the identification of fractionatedelectrograms. Fractionated electrograms, in normal sinus rhythm orduring VT, are usually seen at sites where ablation or other suitabletissue modification will cure VT. However, they are also seen at siteswhere ablation does not cure VT. In accordance with a present invention,once fractionated electrogram sites are identified, VT can be inducedand stunning voltages applied. Sites that interrupt VT are goodcandidates for ablation. Nevertheless, testing at a given site should berepeated because spontaneous interruption of VT commonly occurs.

The three-dimensional electrode arrays shown by way of example in FIGS.2 and 9-13B are particularly useful here. Stunning voltages can besequentially applied to all sites at which fractionated electrograms areobserved. In most patients, fewer than 20 electrode pairs exhibit thismorphologic feature. Even if only one stunning pulse were delivered persecond to these sites, which is a relatively slow pace, a likelyablation site could be identified in only 20 seconds. A sequentialstunning exercise could be performed in less that 20 seconds. If apatient is in VT when the sequence is initiated, one stunning pulsecould be delivered for each heart beat. As VT heart rates are usuallyfaster than 180 beats/minute (or 3/sec), all potential ablation sitescould be stunned in less than 10 seconds. A record showing whichstunning pulse was effective in terminating VT could also be recorded.

Turning to the treatment of AFIB, the physician can create continuouslong, thin areas of electrically unresponsive tissue and then performtesting to insure that the permanent modification of the temporarilyunresponsive tissue would create the desired therapeutic effect. Forexample, the physician can perform the portions of a maze procedure thatare common to most patients and then observe the surface ECG todetermine whether or not AFIB is continuing. In surgical cases, theatrial rhythm can be directly observed, and reading the ECG is notrequired. If the patient has spontaneously converted to normal sinusrhythm or atrial flutter, then the physician can attempt to reinduceatrial fibrillation by burst pacing the atrium at several differentsites. When AFIB persists or is inducible, the physician can use theelectrode(s) to temporarily form one or more areas of electricallyunresponsive tissue. The testing is then repeated and, if AFIB is nolonger present, those areas of tissue can be made permanentlyelectrically unresponsive. If AFIB continues to persist, the physiciancan continue to render areas both permanently and temporarilyunresponsive until a suitable combination of lesions is completed.

In accordance with another aspect of this invention, three-dimensionalstructures (or baskets) such as those shown in U.S. Pat. No. 5,545,193can be used to create an entire maze pattern of temporarily electricallyunresponsive tissue. If subsequent testing does not show that AFIB hasbeen eliminated, baskets that produce slightly different maze patternscan be employed until the proper pattern is identified. The tissue canthen be permanently modified with the same three-dimensional structurethat was used to form the partial or complete maze pattern of stunnedtissue, provided that the electrodes on the structure are configured forpermanent tissue modification. If it is not configured for ablation orother modification, the three dimensional structure can be removed orleft in the body to provide a map of the eventual modification sites.

In accordance with another aspect of this invention, three-dimensionalstructures (or baskets), such as those shown in U.S. Pat. No. 5,647,870,can be used to create an entire maze pattern of temporarily electricallyunresponsive tissue. If subsequent testing does not show that AFIB hasbeen eliminated, then a different set of electrodes can be used tocreate a different maze pattern of temporarily electrically unresponsivetissue and the testing can be repeated. This process can be continueduntil a proper maze pattern has been identified. Then, with thediagnostic basket still in place, therapeutic catheter(s) or probes canbe manipulated to create the maze pattern identified by the diagnosticstunning procedure described above. Guidance of therapeutic catheters tothe desired locations near the basket stunning sites can be facilitatedusing the locating and guiding techniques described in U.S. Pat. No.5,722,416. Alternatively, the same three-dimensional structures may beused to create therapeutic lesions by employing the high-voltage tissuemodification techniques disclosed in Section III-C below.

The effect of a stunning pulse lasts much longer than the amount of timerequired to deliver the stunning pulse. Typically, the effect lasts morethan 100 times longer. Thus, a series of pulses delivered in rapidsequence can be used to create a complex pattern of temporarilyunresponsive tissue. Electrode support structures and energy deliverysystems such as those shown in FIGS. 10-13B, 38 and 39 may be used todeliver a series of stunning pulses. For example, a sequence of 10 msecstunning pulses, with 10 msecs between each pulse, could be applied with50 different electrodes in one second to create an entire set ofintersecting linear regions of temporarily unresponsive tissue. In otherwords, a temporary maze pattern that would block transmission of aexcitation waveform could be created in one second, or less if thepattern requires fewer electrodes. If the temporary maze patternsuccessfully terminates AF, then the physician will know that a curativelesion set for the patient may have been identified. Because stunning isreversible, the successful pattern can be repeated to confirm that theproposed pattern will be therapeutic for the patient.

Arrhythmias can appear when there are gaps in the long lesions formed totreat AFIB or when there is a gap between a lesion and the anatomicalbarrier that the lesion should extend to. For example, during thetreatment of AFIB, lesions are created between the pulmonary veins andbetween the pulmonary veins and the mitral valve annulus. The inventorsherein have determined that gaps in lesions at the mitral valve annulusare common because the myocardium is thicker at this site and becauseanatomical structures at the mitral valve annulus make it difficult toobtain tissue contact that will result in a continuous lesion, even inpatients with easily induced AF or those in chronic AF.

These gaps are very difficult to locate and treat using conventionalroving catheter or probe technology partly because the process ofdefining the location and extent of the rotor circuit is time consumingand laborious. With such technologies, location of the appropriateablation site commonly requires 2-4 hours of procedure time. Use of athree-dimensional structure (or basket), such as those shown in U.S.Pat. No. 5,547,870, can dramatically reduce the time required toidentify a potential ablation site. However, even with this technology,the mapping information does not provide a definitive site for curingthe arrhythmia using tissue modification methods.

The electrical stunning techniques described herein provide an effectivemethod of determining whether ablation at a potential site will cure anarrhythmia. If the flutter is eliminated, the suspected gap areas can berendered permanently electrically unresponsive by ablation or othersuitable means.

In certain situations, an alternative strategy whereby tissue is stunnedat known anatomical positions is more efficient. The approximatepositions of the areas of electrically unresponsive tissue to be createdby the therapeutic catheters can be identified with fluoroscopic orultrasonic imaging. Stunning pulses are then applied to sites that areknown to be probable gap locations based on prior experience. Forexample, unwanted gaps between a line of block and an anatomical barrierare somewhat common, especially at the mitral valve, tricuspid annulusand pulmonary veins. If a stunning pulse applied to the suspected gaparea eliminates the flutter, then the area can be permanently renderedelectrically unresponsive by ablation or other suitable means.

In an alternative embodiment, the physician stuns the selected localregion and then operates the process controller 34 to induce the desiredcardiac event. In this embodiment, the physician observes whetherstunning the selected local region suppresses the undesired cardiacevent. When stunning a given selected region consistently suppresses theundesired cardiac event, which in the absence of stunning occurs, thephysician targets the given region for ablation or other modification.

It should be appreciated that the use of high voltage stunning can becarried out in association with conventional electrocardiogram analysis,without the use of a multiple electrode mapping probe described above.The use of a multiple electrode mapping probe is preferred, as itprovides a more accurate indication where stunning should be appliedthan conventional techniques.

It should also be appreciated that the stunning pulses can alternativelycomprise DC or AC energy transmitted by the electrode 36 from a sourceseparate from the generator 46.

B. Power Considerations Associated With Stunning

The waveform pattern, duration, and amplitude of the stunning pulseseffective to stun an efficacious volume of myocardium can be empiricallydetermined by in vivo or in vitro tests and/or computer modeling.

The character of the stunning pulse is expressed in terms of itswaveform shape, its duration, and its amplitude. The duration andamplitude are selected so as to create a temporary electrical conductionblock without damage to the tissue. For the purpose of thisSpecification, the term “temporary” refers to a time period less thanabout five minutes.

The duration of the pulse can vary from microseconds up to severalseconds, depending upon the waveform (DC or AC) of the pulse, amplitudeof the pulse, and the electrode configuration. There is astrength-duration relationship between pulse duration and amplitude,with short pulse patterns requiring somewhat higher voltages to stun,but not kill, tissue. Short pulse durations not exceeding about 100milliseconds are preferred. Also, because the purpose of stunning is tosimulate the effect of permanent tissue modification, it is important tonote that shallow lesions (about 5 mm) are effective in treating AFIBand some other arrhythmias, while larger and deeper lesions (up to andexceeding 1 cm) are generally required when treating VT.

The pulse amplitude, S_(AMP), selected depends upon the voltagegradient, the configuration of the electrode(s), the depth of tissuepenetration desired, and the impedance of the system, expressed asfollows:$S_{AMP} = {( \frac{S_{V}}{L} ) \times ( \frac{A}{\rho} ) \times R}$

where:

S_(V)/L represents the local voltage gradient,

A is the cross-sectional area of the voltage gradient,

ρ is the resistivity of the tissue to be stunned, and

R is the impedance of the delivery system and electrode that transmitsthe pulse.

With respect to the local voltage gradient S_(V)/L, as a benchmark, DCvoltage gradients of between about 70 volts/cm and 200 volts/cm that areabout 10 milliseconds in duration, when delivered by defibrillationcatheters, have been shown to temporarily stun chicken embryo myocardialtissue in vitro, rendering it electrically unresponsive. The stunning inthese instances extends about 1 cm from the electrode when a 800 volt(DC) shock is delivered. Higher voltage gradients increase the risk ofkilling myocardial tissue. The duration of unresponsiveness of stunnedtissue varies from 1 to 60 seconds and more, depending upon the localvoltage gradient. The effective volume of the local conduction blockshrinks with time, as tissue exposed to lower voltage gradients at theedges of the stunned tissue volume recovers faster than tissue exposedto higher voltage gradients at the center of the stunned tissue volume.See, e.g. Jones et al., “Microlesion Formation in Myocardial Cells byHigh Intensity Electric Field Stimulation,” the American PhysiologicalSociety (1987), pp. H480-H486; Jones et al., “Determination of SafetyFactor for Defibrillator Waveforms in Cultured Cell Hearts,” theAmerican Physiological Society (1982), pp. H662-H670. Based upon theforegoing in vitro benchmarks, it is believed that a nominal voltagegradient of about 125 volts/cm can be safely selected. Voltage gradientsabout four times higher, i.e. 500 volts/cm, are believed to kill about50% of the cells and unintentional application of such voltage gradientsshould be avoided.

The cross-sectional area A of the voltage gradient depends upon theshape of the electrode(s). For example, the portions of the electrode 36shown in FIGS. 1 and 3 and the porous electrodes shown in FIGS. 15-20and 22 in contact with tissue are assumed to be a spherical section witha radius r measured from the center of the electrode body to the tissuewhere stunning occurs. The spherical model is also useful for therelatively small electrodes that are sometimes used in the exemplarythree-dimensional arrays shown in FIGS. 2 and 9-13B. For example, forr=1 cm, the quantity A (assumed to be the surface area of a ½ of asphere with radius r of 1 cm) is 2πr² or about 6 cm². This assumptioncan be made with respect to a porous electrode when the distal half isnon-conductive.

The coil electrodes shown in FIGS. 6-8 and 23-28 form continuouscylindrically shaped transmission areas. The quantity A of the generallycylindrical coil is 2πrl (where l is the length of the coil). When thepatient is on bypass, and one half of the electrode is exposed to air,the quantity A is πrl.

Turning to the resistivity ρ of the tissue to be stunned, for anelectrode exposed to both blood and myocardial tissue, ρ is believed tobe about 200 ohm.cm, while the resistivity of myocardial tissue whenblood is not present (such as when the patient is on bypass) is about400 to 500 ohm.cm.

It is also noteworthy that larger electrodes (greater than about 4 mm)require somewhat lower voltages to achieve the same stunning effect.This is primarily because of decreased losses in near-field tissuebecause of decreased current densities at the surface of largerelectrodes.

The waveform shape and period is selected so that the pulse will notfield stimulate tissue at sites distant from the electrode(s). Astunning pulse that causes far field stimulation can cardiovert (i.e.,stop) the entire cardiac event for reasons other than a temporary,localized conduction block. Cardioversion therefore can overshadow thedesired, more discrete specificity of the stunning effect. The characterof the stunning pulse is selected to induce only a temporary conductionblock in a discrete, relatively small volume of tissue generally equalto the volume of tissue to be ablated or otherwise modified. A biphasicor uniphasic square wave (DC) transmitted for a short duration (about100 microseconds) will achieve this effect. A sinusoidal (AC) signal atfrequencies above about 10 kHz for durations of about 10 millisecondswill also achieve this effect. The DC pulse or short duration AC signalcan be transmitted either unipolar (as the illustrated embodiment shows)or in a bipolar mode.

Based upon the foregoing considerations, and assuming that blood ispresent so that the effective tissue resistivity is 200 ohm.cm, for anelectrode such as that shown in FIGS. 1 and 3 with a diameter of about 4mm, a radio frequency pulse having an amplitude of about 100 volts (at500 kHz) and a duration of about 10 milliseconds will stun tissue to adepth of about 5 mm (which is sufficient when treating AFIB andsupra-ventricular tachycardia (SVT)). With the same 4 mm electrode, alarger pulse amplitude of about 400 volts (at 500 kHz) at a duration ofabout 10 milliseconds will stun tissue to a deeper depth of about 1 cm(which is required for treating VT). Thus, taking typical electrodeconfigurations and typical ranges of stunning depths into account, theradio frequency pulse amplitude (at 500 kHz) will range from about 100volts up to about 800 volts (at 500 kHz), with durations less than about100 milliseconds.

When the patient is on bypass with no blood present (and the tissueresistivity is about 400 to 500 ohm-cm), a radio frequency pulse havingan amplitude of about 50 volts (at 500 kHz) and a duration of about 10milliseconds will stun tissue to a depth of about 5 mm, and a pulsehaving an amplitude of about 250 volts (at 500 kHz) and a duration ofabout 10 milliseconds will stun tissue to a depth of about 1 cm.

Turning to porous electrode structures, and assuming that the distalhalf of the porous electrode is non-conductive so that current flowsprimarily into the myocardial tissue and not into blood, whether thepatient is on bypass or not, the tissue resistivity will be about 400 to500 ohm-cm. For a 1.2 cm balloon, stunning tissue to a depth of 5 mmrequires a radio frequency pulse having an amplitude of about 100 volts(at 500 kHz) and a duration of about 10 milliseconds, further assuming asystem impedance of 70 ohms. At 500 kHz, stunning tissue to a depth of 1cm will require a pulse of about 200 volts for about 10 milliseconds,stunning tissue to a depth of 1.5 cm requires a pulse of about 360 voltsfor about 10 milliseconds, and stunning tissue to a 2 cm depth willrequire a pulse of about 600 volts for about 10 milliseconds. The 600volt pulse may, however, kill 1-2 mm of tissue near the electrodebecause of the very large voltage gradients at the surface of the porouselectrode.

The power requirement calculations for the electrodes shown in FIGS. 6-8and 23-28, which are especially useful in AFIB treatment, have been madewith the following assumptions: the modification/stunning electrodes are12.5 mm long coils, the coils are exposed to blood (effective tissueresistivity of 200 ohm.cm), the current spreads in cylindrical manner,the cylinder is 2 cm long (to compensate for not including the ends ofthe cylinder in the model), and the system impedance is 70 ohms whenstunning through a single electrode. With a cylindrical electrode, thevoltage gradient drops as a function of 1/r. When the tissue surface isabout 2 mm from the center of the coil, a radio frequency pulse havingan amplitude of about 300 volts (500 kHz) and a duration of about 10milliseconds will to stun tissue to a depth of 3 mm. Stunning to a depthof 8 mm requires an amplitude of about 600 volts (500 kHz) and durationof about 10 milliseconds. Beyond 8 mm, the cylindrical model will notproduce accurate approximations of the geometry of the system, andvoltage requirements rise rapidly.

The three-dimensional electrode supporting structures shown in FIGS. 2and 9-13B are also used to stun tissue. Depending upon electrode sizeand spacing, they are generally capable of creating lines of temporarilyunresponsive tissue along a spline or between splines. When suchstructures are incorporated into a catheter-based device, the wires tothe electrodes are typically only about 42 gauge. Although size limitstheir ability to carry high currents for extended periods of time, thewires are capable of carrying the 4 amperes of current required to stuntissue for at least 10 ms.

The current requirements for the electrodes in the three dimensionalarrays are about the same as that required for the conventional 4 mmelectrode discussed above with reference to FIGS. 1 and 3, but thedriving voltage requirements are higher due to the higher systemimpedance. The higher system impedance is caused by the resistance ofthe wires connecting the connector pins to the electrodes (about 20ohms) and the high current density at the electrodes. Assuming thattissue resistivity is 200 ohm-cm (the combined resistivity of tissue andblood in a non-bypass environment), a system impedance of about 200 ohms(we measured this in animals), and the aforementioned spherical model, aradio frequency pulse having an amplitude of about 800 volts (500 kHz)and a duration of about 10 milliseconds will to stun tissue to a depthof 1 cm. A pulse with an amplitude of about 150 volts and a duration ofabout 10 milliseconds will stun tissue to a depth of 5 mm. It should benoted, however, that the destruction of about 1 mm³ of tissue is almostunavoidable using presently available electrodes.

Three-dimensional arrays, such as those discussed in Section II-B, canbe used in conjunction with surgical probes, preferably when the patientis on bypass. The stunning voltage requirements for electrodes in thethree-dimensional arrays are much lower when patients are on bypass. Noblood is present and the effective tissue resistivity is about 400-500ohm-cm. The effective area of the voltage gradient is also aboutone-half of the voltage gradient area when blood is present becausevirtually no current flows in air. The system impedance is, however,increased to about 350 ohms. The net effect is to decrease, by about afactor of two, the amplitude of the voltage pulse required to stuntissue to a given depth. For example, only about 400 volts would berequired to stun tissue to a depth of 1 cm. In addition, the dimensionalconstraints placed on a device that must be introduced percutaneouslyare considerably relaxed for arrays that are inserted into patients onbypass. Electrode area could easily be doubled for devices designed forintroduction into heart chambers via an atriaotomy duringcardiopulmonary bypass. Use of these larger electrodes would decreasethe amplitude of the voltage stunning pulse by an additional factor ofone and one-half, primarily because the system impedance is lower withthe larger electrodes.

It should be appreciated that the relatively high power required to stuntissue will also heat the tissue. As compared to the time required toredistribute heat in the body, stunning pulses are very short induration. Thus, a stunning pulse causes an increase in the temperatureof the affected tissue based solely on the energy dissipated in theaffected tissue during the stunning pulse. Typically, a stunning pulsewill directly heat 2 or more grams of tissue. The maximum power requiredwill be up to about 12,000 Watts, with a pulse duration of 1-10 msec.Therefore, the stunning pulse could deliver as much as 120 Joules to thetissue (or about 30 calories), which would immediately raise thetemperature of the affected tissue to about 50° C.

50° C. is very close to the temperature that can kill tissue. Therefore,unless the goal is to actually destroy tissue (high voltage tissuemodification is discussed in Section III-B), the pulse duration shouldbe limited to prevent ohmic heating to such an extent that the affectedtissue is destroyed. For example, a 1 msec long pulse is nearly aseffective at stunning tissue as is a 10 msec long pulse, but thetemperature rise with the 1 msec long pulse is {fraction (1/10)} aslarge as with a 10 msec long pulse.

C. The Modification Mode

1. Low Voltage Modification

In the low voltage modification mode, the generator 46 transmits lowervoltage radio frequency energy into a selected tissue region througheither the same electrode(s) that are used to stun tissue, or differentelectrodes when the electrodes used to stun the tissue are not suitablefor tissue modification. The radio frequency energy may, for example,have a waveform shape and duration that electrically heats and killstissue in the selected region. When used in cardiac ablation, forexample, the generator 46 is conditioned to deliver up to 150 watts ofpower for about 10 to 120 seconds at a radio frequency of 500 kHz. Bydestroying the tissue, the radio frequency energy forms a permanentelectrical conduction block in the tissue region.

FIG. 5 shows a representative implementation for the switching element80 associated with the generator 46 to change operation between thestunning mode and the modification mode. In this embodiment, theswitching element input 82 (comprising supply and return lines) iscoupled to the generator 46, which delivers radio frequency energy (500kHz) at a prescribed energy input level suitable for stunning, aspreviously described. The switching element output 84 (also comprisingsupply and return lines) is coupled to the transmitting electrode(s) andto the return line electrode, designated E_(r) in FIG. 5.

The switching element 80 includes an electronic switch 92 defining afirst switch path 86 and a second switch path 90.

The first switch path 86 conditions the generator 46 for operation inthe stunning mode. The first switch path 86 includes a first isolationtransformer 88. The isolation transformer 88, shown in FIG. 5 as a 1:1transformer, directs the stunning energy through the electrode(s)without amplitude modification for stunning tissue in the mannerdescribed. In the stunning mode, the electronic switch 92 transmitsstunning energy through the first switch path 86 in short cycleintervals to deliver the energy in preset stunning pulses, as alreadydescribed.

The switching element 80 also includes a second switch path 90, whichconditions the generator 46 for operation in the modification mode. Thesecond switch path 90 includes a second step-down isolation transformer92, which is shown for the purpose of illustration having a step-downratio of 3:1. The transformer 92 decreases the amplitude of the energytransmitted to the electrode(s) to lower levels suitable for ablating orotherwise modifying tissue. In the modification mode, the electronicswitch 92 transmits energy through the second switch path 90 for longercycle intervals conducive to tissue modification.

2. High Voltage Modification

High voltage energy pulses (such as RF pulses) can be used to kill orotherwise modify tissue in at least three ways. For example, thecreation of high voltage gradients within the tissue dielectricallybreaks down tissue structures. In addition, ohmically heating tissuewill coagulate tissue structures, while ohmically heating to very hightemperatures will vaporize tissue.

When voltage gradients at or above 500 volts/cm are induced in tissue,relatively short pulse durations can be used to destroy the tissue.Although voltage amplitudes 4 to 6 times higher than those used to stuntissue are required, the pulse duration requirements are on the order of0.1 msec. As a result, the total pulse energy requirements for tissuedestruction is similar to that used for stunning. In one preferredmethod, stunning pulses are delivered to identify tissue that is to bedestroyed or otherwise modified. After the target tissue is identified,a tissue-destroying RF energy pulse could be delivered.

Turning to heating, a high voltage RF pulse (about 500 to 1200 volts inmagnitude and about 50 to 100 msec in duration) delivers relatively highpower to tissue, thereby enabling very rapid heating. Because the tissueis heated rapidly, there is essentially no convective heat loss duringpower application. These factors allow the thermal impulse response ofthe system to be measured based on the application of a stunning pulse,and the subsequent measurement of temperature at one or more locationson the electrode. From a power control standpoint, the impulse responseof the system provides very important information as to the plant to becontrolled. Short bursts of high voltage RF power, or more conventionalcontinuous RF modification methods, may be used to thermally destroytissue using feedback control algorithms that are optimized with theplant characterization obtained while applying a stunning pulse.

Tissue vaporization can be performed through the use of high voltageenergy pulses with a pulse duration of about 250 msec to 1 sec. Thereare a number of therapeutic applications for this type of tissuevaporization. For example, percutaneous myocardial revascularization(PMR), which is currently performed using laser tissue vaporization, canbe performed by using high voltage pulses to vaporize tissue. Highvoltage pulse-based tissue vaporization techniques may also be useful incertain cancer therapies and to channelize a vessel that has recentlyclotted off.

High voltage pulse-based tissue vaporization techniques can further beused to create a channel in soft tissue in order to gain access to theinterior of a solid organ while maintaining hemostasis. The channel inthe soft tissue would enable a diagnostic or therapeutic function (suchas the formation of an area of modified tissue) to be performed on theselected organ.

D. Roving Pacing Mode

In an alternative embodiment, any of the multi-purposestunning-modification probes discussed above can also be conditioned foruse by the process controller 34 as a roving pacing probe, usable intandem with the basket structure 20 to generate and verify the locationoutput during the above described sampling and matching modes.

In this arrangement, the probe 16 is deployed in the heart region 12while the multiple electrode structure 20 occupies the region 12. Inthis mode, the electrode(s) is electrically coupled to the pacing module48 (as shown in phantom lines in FIG. 1) to emit pacing signals.

In use, once the process controller 32 generates the output location orlocations using the electrodes 24 to pace the heart, the physicianpositions the probe within the localized region near the output locationelectrode or electrodes 24. As above described, the process controller32 preferably includes the homing module 70 to aid the physician inguiding the probe 16 in the localized region within the structure 20.

The process controller 32 conditions the pacing module 48 to emit pacingsignals through the probe electrode(s) to pace the heart in thelocalized region, while the electrodes 24 record the resultingelectrograms. By pacing this localized region with the probe 16, whilecomparing the paced electrograms with the templates, the processcontroller 32 provides the capability of pacing and comparing at anylocation within the structure 20. In this way, the process controller 32generates as output a location indicator that locates a site as close toa potential ablation site as possible.

Due to the often convoluted and complex contours of the inside surfaceof the heart, the basket structure 20 cannot contact the entire wall ofa given heart chamber. The system 10 therefore can deploy the probe 16outside the structure 20 to pace the heart in those wall regions not incontact with the electrodes 24. The probe 16 can also be deployed whilethe basket structure 20 occupies-the region 12 to pace the heart in adifferent region or chamber. In either situation, the electrodes 24 onthe structure 20 record the resulting paced electrograms for comparisonby the process controller 32 to the templates. The process controller 32is thus able to generate an output identifying a location close to apotential ablation site, even when the site lies outside the structure20 or outside the chamber that the structure 20 occupies.

E. Electrophysiologic Diagnosis Mode

The generator 46 can be operated in the stunning mode in associationwith the probe 16 to conduct diagnostic electrophysiological testing oftissue, such as myocardial tissue, in place of or in tandem with themapping probe 14.

In this mode of operation, the physician conditions the generator 46 totransmit through the probe electrode(s) an electrical energy pulse, aspreviously described, which temporarily renders a zone of tissueelectrically unresponsive. By sensing an electrophysiological effect dueto the transmitted pulse, the physician can make diagnoses.

Such sensing is useful in the myocardial area where it can be used todiagnose the cause of cardiac events. For example, by temporarilyrendering zones of myocardial tissue electrically unresponsive using anelectrical energy pulse, and sensing the resulting electrophysiologicaleffect, the physician can, without using the mapping probe 14, locatesites of automaticity, also called pacemaker sites, where arrhythmiaoriginates. Likewise, the physician can, without using the mapping probe14, locate the path or paths that maintain arrhythmia, previouslyreferred to as the areas of slow conduction. Furthermore, by temporarilyrendering zones of myocardial tissue electrically unresponsive using theelectrical energy pulse, the physician can selectively alter theconduction properties of the heart within the localized zone withoutotherwise changing electrophysiological properties outside the zone. Forexample, the physician can create a temporary AV block by operating thegenerator 46 in the stunning mode, as previously described.

Based at least in part upon these diagnostic tests conducted in thestunning mode, the physician can proceed to altering anelectrophysiological property of tissue in or near a diagnosed zone. Forexample, the physician can alter the electrophysiological property byablating tissue in or near the diagnosed zone, as above described, usingradio frequency electrical energy, or laser light energy, or an ablationfluid. The physician can also treat the diagnosed cardiac disorderwithout ablating tissue, using drugs such as quinidine, digitalis, andlidocaine.

IV. Bypass and Non-Bypass Environment Considerations

In many of the exemplary embodiments, the electrodes are exposed aroundtheir entire peripheries. These embodiments are particularly useful whenthe heart is on bypass and there is no blood flow within the heart.Here, air acts as an insulator and produces only modest convectivecooling effects, as compared to a flowing blood pool that has a higherconvection coefficient than virtually static air. Energy transmissionis, therefore, essentially limited to the RF energy that is transmittedfrom the portion of the electrode surface that is in contact with thetissue to either a ground electrode, or another electrode within thegroup of electrode elements. Also, as noted above, the overall impedanceof the system will increase (as compared to a situation where blood ispresent). This is due to the smaller effective surface area between theelectrode and tissue.

Both of these conditions, focused RF energy and low heat dissipationinto the air, will impact the ablation because they result in a highcurrent density. When creating long lesions with a conventionalcatheter, char can be created as the tip is dragged because of the highcurrent density and the difficulty in monitoring tissue temperature andcontrolling power that is inherent in the dragging process. Many of thepresent inventions, however, can take advantage of the high currentdensity because the electrodes are not being dragged. For example, anumber of electrodes can be used to ablate simultaneously because theeffective (tissue contacting) surface area between all of the ablatingelectrodes is smaller and the convective cooling effects are reduced, ascompared to situations where blood is present. This reduces the powerrequirements of the system. In addition, by using electrodes with lowerthermal mass (as compared to a conventional solid tip electrode), lessheat will be retained by the electrode and better temperature sensingcan be made at the tissue surface. This will speed up the creation ofthe lesions and enable better lesion creation control.

In instances where the patient will not be on bypass and blood will beflowing past the electrodes, the portion of the electrode elements (orother operative elements) not intended to contact tissue may be maskedthrough a variety of techniques. For example, a layer of UV adhesive (oranother adhesive) may be painted on preselected portions of theelectrode elements to insulate the portions of the elements not intendedto contact tissue. Alternatively, a slotted sheath may be positionedover the portion of the electrode elements not intended to contacttissue. Deposition techniques may also be implemented to position aconductive surface only on those portions of the spline assemblyintended to contact tissue.

As shown by way of example in FIG. 34, a polymer layer 293 may bethermally fused over an electrode, such as electrode 250, to maskdesired portions of the electrodes. An exemplary process for applyingthe polymer layer is as follows. A segment of shaft tubing is cut longenough to cover the desired electrodes, and is then split in half (orother desired angle) along the axis. One half is placed over theassembled distal section so that it covers the side of the electrodesthat are to be masked. A piece of polymeric shrink tubing, preferablyRNF-100 or irradiated LDPE, is then carefully slid over the catheterdistal end, so that the mask tubing is not moved from its placement overthe electrodes and so that it stops approximately 2 cm beyond the end ofthe tubing half. The distal end is then heated in a controlled heatsource at approximately 400° F. so that the mask tubing fuses into thedistal shaft tubing along its length, and so that all of its edges arewell fused into the shaft tubing, but not fused so much that the coveredelectrodes begin to poke through. Finally, the polymeric shrink tubingis split on one end and the assembly is heated at approximately 225° F.while the polymeric shrink tubing is slowly peeled off of the fusedcatheter shaft.

Additionally, as illustrated in FIG. 35, the shape of an electrode 250′may be such that the metallic material in the region not intended tocontact tissue is eliminated.

The masking techniques described in the preceding paragraph improve theefficiency of, for example, an ablation procedure by decreasing thesurface area of the electrodes and, therefore, the energy required toheat tissue. The masking can be used to form a narrow electrode which issometimes desirable, even when the patient will be on bypass. Theconvective cooling effects of blood flowing by the electrode are alsoreduced. In addition, the transmission of RF energy to unintendedanatomic structures is prevented. This is especially important inepicardial applications when the ablation electrode elements may besandwiched between multiple anatomic structures including, for example,the aorta and pulmonary artery.

It is also noteworthy that masking can be useful during bypass becausetissue can partially wrap around the electrodes when the distal end ofthe device is pressed against the tissue. Such masking can also be usedto control lesion thickness.

Although the present invention has been described in terms of thepreferred embodiment above, numerous modifications and/or additions tothe above-described preferred embodiments would be readily apparent toone skilled in the art. By way of example, but not limitation,methodologies of ablating tissue other than those described above can beused. Laser energy can be transmitted to ablate tissue and fluids likealcohol (ethanol), collagen, phenol, carbon dioxide, can also beinjected into tissue to ablate it (see, for example, U.S. Pat. No.5,385,148). It is intended that the scope of the present inventionextends to all such modifications and/or additions.

I claim:
 1. An electrophysiological method, comprising the steps of:sensing a cardiac event; and transmitting an electrical energy to a zoneof cardiac tissue that temporarily renders the zone of cardiac tissueelectrically unresponsive for at least one second.
 2. A method asclaimed in claim 1, wherein the step of sensing a cardiac eventcomprises sensing an arrhythmia.
 3. A method as claimed in claim 1,wherein the step of sensing a cardiac event comprises sensing at leastone of a ventricular tachycardia, atrial tachycardia and atrialfibrillation.
 4. A method as claimed in claim 1, wherein the step ofsensing a cardiac event comprises placing an electrode in contact withcardiac tissue.
 5. A method as claimed in claim 1, wherein the step ofsensing a cardiac event comprises sensing a cardiac event with acatheter-mounted electrode.
 6. A method as claimed in claim 1, furthercomprising the step of: identifying a target zone of cardiac tissuethat, if rendered electrically unresponsive, would interrrupt thecardiac event; and wherein the step of transmitting electrical energycomprises transmitting electrical energy to the target zone of cardiactissue that temporarily renders the target zone of cardiac tissueelectrically unresponsive for at least one second.
 7. A method asclaimed in claim 1, wherein the step of transmitting electrical energycomprises transmitting an electrical energy pulse to a zone of cardiactissue that temporarily renders the zone of cardiac tissue electricallyunresponsive for at least one second.
 8. A method as claimed in claim 1,wherein the step of transmitting electrical energy comprisestransmitting electrical energy pulses to a zone of cardiac tissue thattemporarily render the zone of cardiac tissue electrically unresponsivefor at at least one second.
 9. A method as claimed in claim 8, whereinthe pulses comprise DC pulses.
 10. A method as claimed in claim 8,wherein the pulses comprise AC pulses.
 11. A method as claimed in claim8, wherein the pulses comprise RF pulses.
 12. A method as claimed inclaim 1, wherein the step of transmitting electrical energy comprisestransmitting energy with a catheter-mounted electrode to a zone ofcardiac tissue that temporarily renders the zone of cardiac tissueelectrically unresponsive for at least one second.
 13. A method asclaimed in claim 1, wherein the zone of cardiac tissue comprises a zoneof cardiac tissue that, when rendered electrically unresponsive,interrupts the cardiac event.
 14. A method as claimed in claim 1,wherein the zone of cardiac tissue comprises a slow conduction zone ofcardiac tissue.
 15. A method as claimed in claim 1, further comprisingthe step of: sensing whether the cardiac event has been interruptedwhile the zone of cardiac tissue is temporarily electricallyunresponsive.
 16. A method as claimed in claim 1, further comprising thestep of: altering an electrophysiological property of the tissue in ornear the zone of cardiac tissue.
 17. A method of suppressing a cardiacevent, comprising the steps of: sensing the cardiac event; andtransmitting electrical energy to target cardiac tissue that temporarilycreates an electrical conduction block in the target cardiac tissue forat least one second.
 18. A method as claimed in claim 17, wherein thestep of sensing a cardiac event comprises sensing an arrhythmia.
 19. Amethod as claimed in claim 17, wherein the step of sensing a cardiacevent comprises sensing at least one of a ventricular tachycardia,atrial tachycardia and atrial fibrillation.
 20. A system as claimed inclaim 17, wherein the step of sensing a cardiac event comprises placingan electrode in contact with cardiac tissue.
 21. A method as claimed inclaim 17, wherein the step of sensing a cardiac event comprises sensinga cardiac event with a catheter-mounted electrode.
 22. A method asclaimed in claim 17, wherein the step of transmitting electrical energycomprises transmitting an electrical energy pulse to target cardiactissue that temporarily creates an electrical conduction block in thetarget cardiac tissue for at least one second.
 23. A method as claimedin claim 17, wherein the step of transmitting electrical energycomprises tramsmitting electrical energy pulses to target cardiac tissuethat that temporarily create an electrical conduction block in thetarget cardiac tissue for at least one second.
 24. A method as claimedin claim 23, wherein the pulses comprise DC pulses.
 25. A method asclaimed in claim 23, wherein the energy pulse comprise AC pulses.
 26. Amethod as claimed in claim 23, wherein the pulses comprise RF pulses.27. A method as claimed in claim 17, wherein the step of transmittingelectrical energy comprises transmitting electrical energy with acatheter-mounted electrode to target cardiac tissue that temporarilycreates an electrical conduction block in the target cardiac tissue forat least one second.
 28. A method as claimed in claim 17, wherein thetarget cardiac tissue comprises a slow conduction zone of cardiactissue.
 29. A method as claimed in claim 17, further comprising the stepof: sensing whether the cardiac event has been interrupted while thetemporary electrical conduction block exists.
 30. A method as claimed inclaim 17, further comprising the step of: altering anelectrophysiological property of the tissue in or near the targetcardiac tissue.